IANAL, and I'm not affiliated with Stack Exchange (so, basically, I'm "some loud-mouthed guy on the Web"), but where exactly does SE enter into it? "I posted that guy's comics, so now it's your job to judge if it was okay or not, because, well, it's your server?" That doesn't make sense to me (maybe because IANAL?).
See also the legal thingy (which is linked on every page): "Subscriber (...) agrees that it will not contribute any Subscriber Content that (a) infringes, violates or otherwise interferes with any copyright or trademark of another party (...), (c) infringes any intellectual property right of another or the privacy or publicity rights of another (...)" - subscriber, that's you; it doesn't say "SE will police its users to see if they're breaking some law somewhere" - IMHO it says "users are supposed to be aware what they're doing".
The problem is, if SE started policing some stuff, they'd have to police the whole network, and possibly be liable for infringements. See a very similar discussion at Should moderators enforce NDAs for software vendors?