This is my argument against your blanket statement. Genetics determine the best nutrition for each individual person, not ideologies or beliefs.
http://www.dadamo.com/txt/index.pl?1039
Just because we "could" replace all those nutrients with veggie based one doesn't mean we should. Not for everyone.
I will say that you are correct that most meat humans eat are from "factory farms" or from, really, inhumane conditions. As a farmer I strive to give my animals a good life while I have them, before I butcher them for my own families consumption. I raise sheep and chickens but have associates in our co-op who raise beef on pasture. They pay nothing for feed and input no antibiotics or hormones into their cattle. They have a happy and normal life, so there are exceptions to everything.
Yes it is a blanket statement, but it is for the most part true. Everybody knows there is always an exception, i don't care about the exceptions i care about the majority causing the problems. All that link shows is that people need different levels of nutrients, it said nothing about some people needing meat where the majority of the rest of us would be better off without it. We're all human genius, we all need the same stuff, we just need it in different amounts that's all that said.