Vegetarians more likely to have mental issues...

[homelycooking]

Supposing that animals actually do have rights, the most fundamental among them would certainly be the right to life. Would every member of Kingdom Animalia be entitled to these? What would the human responsibility be to protect those rights? Do animals have rights protecting them against intra-species violence, or merely against the slings and arrows of Homo sapiens? It's a concept too problematic to be meaningful.

I think that animals have "deserts", i.e. a measure of respect owed to their autonomy and intelligence. This is a far more subjective and fluid concept than the idea of rights, though a more accurate one, since the idea of rights is incompatible with the occasional human need to kill animals. The concept of desert requires that when killing animals is unnecessary, humans should refrain; similarly, our treatment of living animals ought to be more reverential than it is repressive. Otherwise, animals generally deserve to be left unmolested.

In this mode of thought one can find plenty of zoocentric justification for vegetarianism, though I think there's probably a stronger case to be made for an anthropocentric justification. Humans would probably be better off, to say nothing of other animals, if we ate less meat. Energy, water and land could be used more efficiently, calories could be produced more cheaply and on a broader scale, and no one would have to live downwind of a lagoon of pig shit.

n.b. Be wary of conflating "animals" with "mega-" or "meso-fauna", though certainly there's an unconscious temptation to do so.