High quality meat is irreplaceable in the optimal human diet.
EDIT: I'm a vegetarian. I'm well aware there are nutrients that are harder to get on purely plant-based diets, but it's far from impossible. I'm getting my Omega 3s (all DHA and EPA, not merely ALA) from algae, and my B-12 from plant sources, too.
What am I missing by not killing sentient things for sustenance?
I'm sensitive to the moral issues involved, and understand the arguments against eating pigs and cows; however, I think it's reasonably ethical, and biologically optimal, to at least eat fish and eggs. And no matter what, farm animals should be raised humanely (pasture farms, not factory farms).