Like, he doesn't abandon Dudley to the Dementors. To me, that's sort of a situation where you'd just have to do something--you'd have to be be "criminally negligent" or have "depraved indifference" or something in order to just walk off.

Plus, there's the fact that not only would he get in trouble in the wizarding world (if he even got out of the situation with his soul intact), but that his aunt and uncle would refuse to shelter him. While this sounds like a "good thing", it actually isn't, if we're to believe that Dumbledore's statement about bloodlove magic has any credence.

But to me, being against EVIL (whether embodied by Slytherins, or, um, wolves

Actually, wolves aren't all that evil. They just get a bad rap in symbolism but they're actually quite necessary to the ecosystem, being the top predators or something... oh. Yeah, the comparison makes sense.