In the dresdenverse there are a lot of powers keen on making sure "Free Will of Mortals" or "The Mortal Ability to Choose" is enforced.
The in-game mechanical effect of first (killing), second (no transforming), fourth (no enthralling) are likely mechanically enforced by the Power that entities like angels, the Knights, etc serve, and the extra power is a form of sponsored push by the kinds of folks who power the Denarians, at least two of the vampire courts and ghouls. The 5th is probably also linked to this, as necromancy (as opposed to ectomancy) seems to deal with actual souls of mortals, not just a "footprint" left behind by their life, or just their bodies. Although some necromancy doesn't seem to fall afoul of this (purely animating dead bodies) this would indicate why it is NOT a violation to animate the body of something that never had a soul.
The other 3 laws don't strictly apply to mortals with souls, but seem to apply to everything.
The events in Cold Days would indicate that at least one extremely powerful group of entities is interested in enforcing the 7th law (don't even THINK about dealing with outsiders). Blame the mechanical effects of that on....read the book. The slippery slope aspects of it fall under the opposition.
I'm less clear on the 3rd (reading minds), and 6th (time). My guess is actually it's the White Council who is enforcing these, for reasons of their own, as the original Merlin clearly did muck with Time, and the Gatekeeper and Blackstaff are exceptions in various ways, plus all Wizards get a bit of prophecy as they age. The slippery slope side may have roots more in just an addiction wizards tend to get to the behavior (invading privacy or trying to fix mistakes in time with more meddling).
The political side (Wardens show up etc) is much more legalistic, and usually the error is on the side of "caution" although there is clearly a procedure that includes a soulgaze to help determine if the person is too far gone to be saved.
If I was going to change the mechanical behavior (get a boost when being bad, at the cost of becoming closer to an NPC or actually becoming one) I'd want to be damn sure I knew what the reasons for the laws were in my universe, and the purpose they serve to the cosmology. Above are my guesses, and it would inform whether or not a person had to take a lawbreaker power, or whether they'd get by with a consequence or aspect change on a borderline violation...or whether much to their surprise nothing happens aside from any remorse they might naturally have for such an act.