I know some vegetarians and vegans, and they have to use massive amounts of vitamins just to get all the stuff they would normally get from a single chicken sandwich.
Then tell them to eat better. All the major nutritional organizations agree that you can get everything you need from a balanced vegetarian or vegan diet. Obviously if all you eat are carrots, you're going to be in pretty poor health. Getting a good mixture of vegetables, grains and legumes isn't any harder than getting a good mix of meats, grains, vegetables and dairy (actually, having spent a long time as first an omnivore, then a vegetarian and then a vegan, I can safely say that being vegan is way easier).
The problem is that most people either never try a vegan diet because they think "OH NO HOW WILL I GET MY PROTEINZ!?21one," as if their current diet of cheetos and beer is somehow optimally attuned to their demanding lifestyle of hitting refresh on blogs and pretending to work, or they make a very half-assed attempt by spending a week eating nothing but cucumber and celery sticks before giving up and declaring that veganism is 'impossible.'
Ugh. I need an auto-responder for these:
I suppose the my biggest problem is that vegetarians claim that animals can have feelings, but apparently the plants can't. I suppose maple trees enjoy getting giant hoses stuck up their trunk so that their life force can be sucked away? They're incapable of defending themselves, too!
Plants don't even have nervous systems. In contrast to animals (mammals especially), whom we understand to function on a relatively similar level to humans: i.e., they feel pain, they appear to react to the loss of family or pack members, they display a noticeable fear of death (imminent death, at least: I wouldn't suppose they have existential angst). Plus, clearly you do not believe this is true, as unless you have mad scurvy, I'd assume you eat both plants and animals. If you are concerned about other beings because of how they think and feel, even if you are willing to prioritize humans over other animals (which I think is reasonable), it's entirely justified to say that you would prefer to avoid damaging thinking animals as much as possible, given that it isn't particularly a lot of work, anyway.
Even more than that, trees are in more danger than animals are currently. I'd rather have a couple pigs for dinner, rather than only eating corn or rice, so that more rainforests in Brazil can be chopped down to make room for plantations.
Uh, what do you think farm animals eat? Sunshine and rainbows? Do you have any idea how much extra grain we need to grow to sustain livestock in North America? We could feed like ten North Americas with all the food we are feeding to cows so we can eat them.
The fact is, the only reasons to eat meat are flavour (which is really only a factor for about six months of vegetarianism, as your body will actually change your tastes to correspond to your available diet) and convenience (vegan cooking at home is easy, but restaurants sometimes seem to believe that vegans just eat salads). If you want to eat meat, go nuts. I'm not going to stop you, but there isn't much point in making up other crazy excuses.