I think that is exactly the point. It doesn't matter whether magic is involved or not, as I suspect Sin (or something like it) exists within the world of the Dresden Files. By which I mean, evil. But the source of it is the question. Is it from the Outside? Is it from the Devil? Or is it generated by mortals? Very tricky to answer without more knowledge.
But I wouldn't say the Laws of Magic exist merely to preserve the White Council's good image. The only people who would care are other mortal practitioners. No, I think that the Laws truly were made to stop wizards turning into demigods and violating the free will of mortals. Whether they actually achieve that is still questionable, and as often shown and discussed, they don't really deal with right and wrong.
I suspect it isn't so much that they don't care about heinous acts as they are very careful about how they define it. Lucio's discussion with Dresden was very illuminating.
To use your example (and I just want to point out we are skating close to the line of Touchy Topics so let's just all be careful here), a wizard paedophile who wasn't violating any of the Laws or Council rules would not be subject to their punishments. Not only that, but defining such a character is more tricky than you might imagine. The age of legal marriage varies greatly across the world even today sadly, and while generally most cultures in most times consider prepubescent people children (and therefore consider any sexual relations with them paedophilia) unfortunately it isn't always the case. When you get then factor in other time periods as well where people got married earlier and lived shorter lives...it becomes even trickier. I bring this up because there would be wizards alive on the White Council who might come from a time and place who don't see the issue with marrying a 14 year old or whatever. And they wouldn't even necessarily be in the minority, as it seems the Council's average age is around a century or more.
So disciplining such individuals wouldn't only be difficult, but probably considered outside the scope of the White Council's remit. Unless of course they used magic. In which case I suspect there would be many wizards who would take great satisfaction from going after such monsters.
What is suspect is a really interesting question is whether such monsters, if they don't use magic to carry out and/or fascilitate their abuse, would their magic end up warping to black magic? My guess would eventually be yes, but the Laws don't cover that. I guess what I am saying is that while using black magic will warp and individual faster, a person not using black magic will still become warped by doing evil deeds, even if they don't end up becoming a gibbering warlock in appearance.
There is a qualitative difference in how black magic changes a mortal than committing evil through mundane means. As I said above, you can't use the forces of Creation without consequences.
It would be a very interesting area for the books to follow, I agree. I think Jim would do a good job of it and treat the subject matter respectfully. And the next book would be a reasonable place to do such a thing, although I suspect Harry might be a bit busy dealing with his own trauma and and fallout. But hey, it could be a subplot. Otherwise a short story might work. Then again, Jim might want to avoid the potential minefield. Which is understandable.