Is it really rational to make dog-fighting a felony, but then to permit the slaughter of cows and pigs in oft-inhumane conditions? I suppose that the distinction is that cows and pigs provide food to humans, so there is some utility in their killing, but dog-fighting provides no utility other than base-level entertainment. And is the possibility of eating venison the reason why hunting is legal, but dog-fighting is not? There is probably also a distinction that dog-fighting is inevitably very painful for dogs, whereas a deer being shot by a hunter or a cow being slaughtered in a meat-packing facility creates less suffering for the animal, although I suspect that in practice, the difference is not too great. Finally, there is no reason why protection of some animals is illegitimate because we don't protect all animals in the same way.
All that said, after reading the indictment, there is a distinguishing factor between generic cruelty to animals in the meat-packing industry and what Vick is accused of. When Vick was supposed to be a passive investor and/or a guy who went to a couple fights, but didn't have significant involvement in running the operation, then the analogy made sense. Vick was participating in a cruel enterprise, but meat-eaters are sitting in a glass house when they throw around those charges. Now, assuming that the facts in the indictment are true (and the Feds are typically zealous about not throwing around accusations that they can't prove), Vick participated in every aspect of the operation. He didn't just pay for the facilities at which the fights happened; he tested out young dogs for aggression and then bludgeoned, electrocuted, or shot the ones who didn't perform. That goes beyond being a passive participant/meat eater into someone who can perform inhumane acts without batting an eyelash. There's a psychopathic element there that pushes Vick down the continuum of moral culpability. (Insert standard caveat that Vick has not been convicted of anything yet and he could just be guilty of keeping the wrong company, blah blah blah.)