1) A wizard killing a human gets Lawbreaker. A wizard killing a nonhuman does not. Why? Do they believe any less in killing with magic? Would they destroy any less of a person if they burned Thomas to ashes or ripped Lily's heart out of her chest?
Things without free will are in many ways animals (or forces of nature) that can talk. You can't rehabilitation something without free will. If something presents itself as sufficiently dangerous, you kill it, or failing that try to banish or contain it.
Free will represents possibilities and potential. And killing that leaves a scar. And the more scarred you become, the more monstrous.
Killing a mortal (free-willed individual) in self defense still gets you a lawbreaker (1st). It just doesn't result in a beheading.
But kill a red court or black court vampire and who cares? All it was going to do is kill, drink blood, and maybe create more vampires.
As to why killing White Courts doesn't violate the first law. It probably depends on the white court vampire and the situation. Killing them when they are hunting is fine (the demon is pretty close to the surface), but killing one when he/she is sun bathing on its rooftop is probably a no-no. I think in this very specific case (it is an outlier) Mouse's perspective is the right one.
Mouse growls at Thomas's demon, not at Thomas.2) A wizard using mind-magic gets Lawbreaker. Molly believed that what she was doing, using her magic to help someone else, was good. She did not know of the damage it could do to others so there is no way that factored into her beliefs. So why, exactly, is she more monstrous for believing in something when, to her knowledge, it had no drawbacks at all?
Same as above. Mindbending, in some ways, is even more dangerous that killing. Because if you mindbend a non-human you are exposing your mind to its mind and who knows what messed up stuff goes on in there.
3) Let's look at Kumori. Lawbreaker - Fifth. She believes that death is something one should fight against and ultimately conquer. And she is more monstrous for it. Come again? Isn't that what thousands upon thousands of doctors all around the planet are trying to do? Isn't it there in a certain book that death was not part of the plan, is a very bad thing, and it will be ultimately conquered?
Playing god always twists a person's brain. Hence the lawbreaker. Even if someone didn't use Kemmlerian necromancy. Heck, even under the condition that someone made themselves a "living dead" humans (why is it "humans" and not "humen?") it is still twisted.
But I still thing that sponsor magic should suffer all the same non-political drawbacks of mortal magic. You accrue lawbreakers (and if your sponsorship doesn't result in accord protection, you might face political consequences too). Using sponsored magic to do horrible things means you are working for a person that approves of those horrible things (maybe even wants them) and you are enabling that behavior. You are taking in that malevolence and aiming it at another being of possibilities.
As I said before, mortals aren't just strings on Fate's loom, as Harry witnessed when he soulgazed Molly, there were many avenues should could move down.
Just now it occurred to me that maybe the reason "monsters" can't be gazed could be that they
don't have the choices mortals have (therefore there is nothing to gaze). They follow the path their nature dictates, and therefore they don't have to see what is ahead or reflect on what is behind, for them there is only now.
And yes, it is possible that some "pure-mortals" default to being monsters. A reinfield pop into mind. But it could also be a person that has just stopped viewing others as people and just gone dark. Like Cowl and Kumori. Going refresh negative is supposed to represent loss of humanity (and free will, YS66 "This is the dividing a mortal's free will from a monster's unnatural compulsions"). I don't think killing those character represents a law being broken nor would turning them into fluffy bunnies (unless turning a cat into a mouse was a lawbreaker).
So:
1. The first time a particular law is broken, you get Lawbreaker (xth) [-1]. Bringing you closer to negative refresh.
2. The second time a particular law is broken, you get Lawbreaker (xth) [-2]. And you change a permanent aspect.
3. The 5th (and ever 3rd time after that) you break the same law, you change another permanent aspect.
Sum: Max of -14 refresh and at least all 7 aspects changed. Easier to be compelled to be bad (fate points) and easier to tag to be bad.
Result: MONSTER.
This is why the political consequence of lawbreaking is summary execution. A guy with only a single Lawbreaker (xth) [-1] is easier to kill that same guy a few years later that has broken the same law 25 times (refresh -2, and all 7 aspects changed).