My personal thoughts on the matter are that it's not that there is some kind of being or guardian of the Laws. The Laws and the consequence of breaking them are natural phenomena like when you throw a stone, gravity will act upon it and it will eventually fall down. There is no Spirit of the  Higgs Boson sentiently acting to make it fall, it's a feature of the universe we live in.

For the Dresden Files, the Laws and what happens when you brake them is a consequence of two fundamental properties of the Universe being forced to work against each other. First off, magic is the energy of creation left over after the universe came into existence, this has been stated at least ones by Dresden directly if not multiple times. Second, mortal Free Will is special, while other creatures have more or less leeway in their actions humans are the only beings in the whole of existence that can say that they are truly of Free Will.

Now let's look at the Seven Laws of Magic through the lens of Free Will, shall we?

       
    "Thou Shalt Not Kill" - easiest, killing someone prevents them from executing their Free Will anymore
    "Thou Shalt Not Transform Others" - forcing someone out of their human body that holds Free Will, limits it in an obvious way (it might even suggest that Free Will is something biologically/metaphysical to the human body)
    "Thou Shalt Not Invade the Mind of Another" - directly influencing and breaking someones Free Will
    "Thou Shalt Not Enthrall Another" - indirectly influencing and breaking someone's Free Will
    "Thou Shalt Not Reach Beyond the Borders of Life" - bringing back human souls, capable of Free Will, and binding it to your will
    "Thou Shalt Not Swim Against the Currents of Time" - going back in time to unmake Free Will decisions
    "Thou Shalt Not Open the Outer Gates" - that one is just there so that no one brakes the Universe by accident (looking at you Dresden)

So my theory goes, that the Taint from practising black magic comes from the crash of two fundamental elements of the universe. You are using magic (the force of creation) to unmake/damage Free Will (a building block of creation) the negative feedback from that damages reality in the form of your psyche giving the black magic corruption effect.

So it's a natural phenomenon, no gods or convents necessary. Just a sideproduct of how the Dresdenverse is set up.

Cowl has been playing with necromancy and outsiders.  A lot.  I am sure he is taking all sorts of precautions, but I suspect there is a limit to how much he can shield himself from the consequences of that.   I suspect Cowl's magical energies are starting to show as tainted. 

Point of order, Cowl seems not to have any direct contact with Outsiders. In his fight with Dresden Harry notes that his magic lacks the usual

nauseating, greasy, somehow empty feel that I'd come to associate with the worst black magic.

Butcher uses this kind of descriptives almost exclusively for Outsider influence/magic. Stands to reason that Cowl doesn't have direct contact with Outsiders, or at worst is so skilled with his magic that he can avoid being tainted by his contact with them.

But back on the topic, I agree with most reasons stated here. Freedom to act without any scrutiny being a big one, and as most people said being the Councils expert on Vampire he would have been in high demand during the War.

His Vampire expertise is one too but in a different way. Every time we see a Cowl sponsored plot going on, vampires are somewhat connected to it.

Dead Beat - the offensive of the Red Court was scheduled with the Dark Hallow.

White Night - Cowl was the one to steer the Skavis into betraying his Court.

The whole plot showed a deep understanding of White Court Vampires psychology, which as Ramirez mentioned is NOT common knowledge amongst Wizards or Warden. It is actually so suspect to understand a White Courts psyche that it was enough for Ramirez to suspect Dresden of backdoor dealing with the Court when he showed it. So this definitely implies that Cowl is a Wizard with above standard knowledge of at least the White Court - say like Simmon the Council expert on Vampires.

His style of magic, but this one can honestly go both ways for Simon or Justine so I guess it doesn't really count. Harry uses an x shape of his wrists as a defence posture, so does Cowl. If Simon taught Justin and Justine taught Dresden what he knows about battle magic. It makes sense for both of them to have similar gesture. And no, crossed wrists are not a standard position because we see Peabody in Turn Coat using the Doctor Strange gesture as a defensive Sigil.

So, these are Mab's 'evil' qualities?  Her epic level of torture for a traitor who nearly destroyed the balance of the world forever (and arguably could have killed it), murder, and her drafting of young fae to grow up to be soldiers?  I mean, she's not a saint or anything - but the Denarians, less evil than Mab?

That's my whole point, they are at worst equal evils, but everyone says the Mab is the lesser/predictable evil. And from a power standpoint, it makes much more sense to pick up a coin then taking up the Mantle, which I explained earlier as well.

Do you remember what Nicodemus' plans were in Death Masks?  To take an absolutely horrific plague that killed everyone that caught it in horrible, twisted, torturous ways, and to go to O'Hare Airport and spread it across the nation, and to the rest of the world.  To basically have a worldwide pandemic, killing billions in excruciatingly painful, torturous ways, to kickstart the apocalypse.  And that was just one of their many twisted plans that they've done through the millenia.

You could certainly argue that his plans in Small Favor weren't so horrible, but that's only because Nicodemus doesn't go out and state what he wants to do with Ivy.  It's clear what he can do with Ivy; like start a nuclear holocaust.  Or bring some Old Ones back into existence.  Granted, the second one isn't probably likely, but the first one is directly in line with his original goals.

That's the problem with not going his real end goal. Yes, a couple of millions of people dead is bad (since billions is an exaggeration, the plague was a conjured bacterium so it needed constant energy flow to keep existing, and the fake shroud wouldn't have had enough juice to sustain it beyond 1-3 sun rises). But do you think there will be no casualty during the BAT?

Who knows once the book series is complete if Nic's alternative plan of "kill a couple million" will look like a rather nice alternative.

Well, yes, the Aquarium scene does pretty much state that he's aware of Nemesis and that he works against it.  But that's far from saying that Nicodemus' ultimate goal is to stop the Outsiders.  He never goes so far.  All he really demonstrates is that he recognizes them as another power, similar to the Red Court at the time, which he is shocked and infuriated to learn has infiltrated his ranks.

The scene does more than establishing that he knows about them. He is in strict opposition to them and is against all reality threatening plots. In the great scheme of things, he is as much a force for good as is Mab.

Did you just hold up Mab's contracted drafting of fae children into her army as an evil event, but then hold up an act which emancipated an entire nation of slaves as a Captial E Evil?

No. I am saying that, again, that Mab and Nic are at worst equal in their evilness. And that the murderers *unnecessary* acts of violence that TWG does, strips him and his side of any moral superiority. So saying that Denarians are evil just because they oppose TWG isn't a real argument. You have to show me that they have truly evil intentions. Because so far they have been doing stuff that Mab and TWG have been doing too, and probably for the same reason, fighting Outsiders.

And not to go all theologian on you but:

And the LORD hardened Pharaoh's heart, and he did not listen to them, just as the LORD had spoken to Moses.

So yee WG is a bit of prick here, not only killing babies but also mind controlling the pharaoh in to not agreeing so that he can torture him some more. Not to mention the fact that as an omnipotent being he could just teleport "his people" out of Egypt no killing necessary but that wouldn't apparently be fun enough for him. Or the fact as you mentioned yourself waiting for generations of their suffering before acting. Got to soften them up so they will worship you more once you rescue them, hmm?

In the end, the situation is as following ALL 3 sides Denari, Mab, TWG have been doing disgusting and vile things for centuries if not millenia. Presumably all to either fight the Outsiders or to strengthen and widen their own power. But yet for some reason, Nic and the Denari are seen as some unredeemable E Evil, while Mab is a strict aunt and TWG is a paragon of good. With nothing to really distinguish them from each other if you take away the 2000 years of PR campaign, the Church has been running.

Honestly, the whole argument that Mab is the lesser evil doesn't really make sense to me. Let's compare the two:

Winter Knight
- you only get power, some supernatural strength, and painkiller. All tied to your position of Knight
- you have a constant 24/7 temptation of the instinct that the Mantle awakes in you
- there is literally only one person in the history of mankind that managed to get out of this position alive

Knight of the Blackened Denari
- you get a power boost via Hellfire (and maybe in Dresdens case at this point he could have both Hell and Soulfire) which is directly tied to your position and a Coin holder, you are functional immortal, and you get superb healing no faking via painkillers, but most importantly you get knowledge and magical experience beyond the reach of ANY creature on the planet. This is where the real power boost of the Denari lie, and if you ever leave you get to keep that knowledge.
- the only temptation is intellectual, yes Lash might converse with your subconscious but at the end of the day, those conversations are also based on logic and reason. There is a whole world of difference between being tempted on an instinctual emotional level, and being tempted on a logical Socratic level. IMHO it is much easier to withstand the later than a constant nagging from your urges.
- there is literally a world spanning organisation dedicated to helping you get rid of the coin (and as mentioned if you leave you keep most of the power boost anyway) so your odds of getting out alive are astronomically higher

If you are looking for the best power boost, with the highest chance of retaining yourself, and best odds of surviving and leaving it behind, Denari win out against Mab.

I've been thinking about Harry's future, and he wont make the Senior Council during the series. 

My personal WAG? Once everything is set and done, the BAT is survived etc. There is no White Council anymore. There is the Paranet and its highest position is the Dresden.

I still wonder, once the WC was officially at war with the Rampires and thus they were fair game under the Accords, Eb didn't drop satellites/chunks of asteroid/earthquakes/etc on every Rampire stronghold? Being able to throw around Tunguska Events just seems too overwhelming - I don't see what anyone short of god/cosmic level powers could do to defend against it.

Because the Blackstaff doesn't officially exist, so his actions need to be framed in a way that gives the Council political deniability and coverage. Yes, every organisation has a wet works man, but most of them don't admit it since by definition it is a person who is there to break rules and agreements so having his existence be official would make your deals and agreements less valuable.

Because the whole potential situation is mortals using their Free Will to make decisions.

Free Will is a bitter sweet gift, and this are the downsides of it, humans can be wrong. If Merlin made the Free Will decision to execute Molly TWG wouldn't intervene the same, as he wouldn't stop Michael from drawing the Sword and attacking the Council for it. But the Sword wouldn't have any power besides being a sword since he doesn't use it with a) clean intentions (vengeance) b) in the way the Sword are supposed to be used (in protection of mortal Free WIll)

This whole situation simply doesn't fall under the purview of things where TWG and Angel intervene. The precedence where they do are clear and established, infringement on mortal Free Will by supernatural powers, or supernatural powers going against their intended purpose.

Yes TWG stacked the chances in Mollies favour (Dresden's belief, the arrival of the rest of the SC saved by Michael) but in the end, this is all he can do. In the end, it is mortal will against mortal will. TWG, Angels, and the Swords have nothing to do in this conflict.

The Swords have a specific purpose and a specific set of powers.

They come into action when they are against a supernatural power that infringes on mortal Free Will or are up against a supernatural power that acts against its intended nature. Wizards don't fall under any of this categories so the Sword wouldn't give Michael any powers and he would end up a splatter on the wall.

And even if by some miracle (he, he, see what I did there) he would still get the Sword's power it doesn't make him invincible. The Sword's power is to level the playfield on the supernatural front. It would still be Michael vs Morgan, both skilled sword fighters, one of them with almost a century of experience. I give that one to Morgan, so again Michael would die, even with Sword support, which it wouldn't give him in the first place.