I say this as a confirmed meat-eater, but I'm pretty certain that when people look back on our era from 150-200 years in the future, they're going to find the widespread habit of consuming the seared flesh of mammals raised for the slaughter to have been a bizarre and barbaric practice. Thus, I've been reading with interest some posts kicking around on the subject of animal cruelty laws.
The conversation's been noteworthy for mostly playing out on libertarian blogs, which has, I think, closed off some possible avenues of conversation. It seems to me, for example, that one main reason we forbid cruelty to animals isn't because we're against cruelty to animals but because we want to discourage cruelty. If your friend liked to lobsters for fun, you'd worry. And not just for the sake of the lobster (I don't think arthropods have real nervous systems) but because people who get their jollies from torture seem dangerous. You'd worry more if he was torturing mice, and even more if he was torturing chimps. Maybe this is why we tend to come down much harder on cruelty per se -- hurting animals for the sake of hurting them -- than we do for instrumental meanness, subjecting them to bad conditions for the sake of making meat cheaper at the supermarket.
I don't think that line of reasoning works on libertarian terms, but since most people don't adhere to lunatic fringe ideologies, that's probably what's motivated a lot of people.