In a modern age where dietary supplements come in bottles (of pills), a vegetarian or vegan can survive without nutritional issues. However, in the absence of such supplements, vegetables don't provide EVERYTHING you need to live. Some meat proteins (and more important, certain types of fats) are necessary for good health. If you can't afford the supplements, then you have to try for the meat (though that ain't cheap these days either). I wonder if vegans aren't somewhat elitist food snobs because THEY can afford the supplemental stuff that many hard-working people can't.
As to me, there is nothing wrong with red meat, white meat, fish, frog (legs), alligator (tail), poultry, etc. For textural reasons I scrupulously avoid escargot, salmon, and insects. (There might be a few things I unscrupulously avoid, but let's not go there.) I have dietary issues since my gall bladder and I have parted company, so really oily meats are things I have to avoid. Sadly, 90% of my favorite pizza toppings fall into the "avoid" category and pizza without meat is like a country girl without a few freckles (as the old saying goes.) So no more pizzas have to give their lives for me. That dietary problem also means that I have to avoid nutria (a.k.a. coypu) - they are greasy. Which in a way is a shame since they are quite prolific here in south Louisiana. There are only two differences between nutria and tribbles - (1) tribbles make nice pets and (2) nutria aren't born pregnant.
As to moral reasons, hate to break it to the vegetarians and vegans, but even if people didn't eat those critters, they would die in huge numbers due to starvation (due to their overgrazing) and suddenly increased predator numbers (due to the law of supply and demand applied to nature). Controlling a herd to live within the capacity of its grazing area is important. So... you thin out the herd by killing a bunch. So NOW what do you do with the carcasses? I contend that if you are going to play the morality card, then those animals died in vain UNLESS you eat them so that they can take a more active part in the great circle of life. (Echoes of Sir Elton singing in the background...)
