I'm a vegan, and I've heard all the uneducated comments about how bad it is to not eat meat, that we HAVE to eat meat to survive, that we will need to take protein pills (which don't exist... so what do these people really know anyway?) if we don't eat animals.
But I've never heard one good justification for eating meat, otherwise I would have less conversations that sound like this:
Joe: Meat is good
Me: Why
Joe: it's got protein
Me: name something without protein
Joe: Uh, meat isn't bad
Me: What about cholesterol and high fat content? Parasites and carcinogens? The pain of the animal?(if they are capable of empathy)
Joe: There's no proof of that
Me: Only scientific studies that link high cholesterol and fat intake to heart disease and kidney failure. Also it's true, the animals are killed before you eat them.
Joe: But it says here at MeatisGood.Beef.com that's not true
Me: it's funded by the beef industry, it says so on the front page
Joe: You're a vegan-nazi
Me: a what?
Joe: you're forcing your views on me!
Me: Ah, you started the whole conversation, and is discussion bad?
Joe: ah, no, PeTA sucks! I saw it on TV
Me: What does that have to do with our conversation?
Joe: (fingers in ears, eyes closed, stomping feet) LA LA LA LA LA I CAN'T HEAR YOU! Runs away....
But I forgive them because bad habits are very hard to break, and good habits are hard to cultivate and maintain. There's one thing I know for sure doesn't have a very positive effect, and that's to make people feel guilty about what they're doing. They may listen and change their eating habits for a while, but in the long run, there's a great chance they're only ending up getting annoyed by whoever it is who makes them feel guilty.
Things to consider;
Family values (Mom loved you and she gave you meat to make you strong, she knows what she's doing and she woudln't give you anything unhealthy)
Religious upbringing (you may have been told that God gave you these animals to eat, that the earth and it's creatures are yours to use at will, my interpretation of that misconstrued line is we were meant to be stewards to the earth and its animals, not enslave it)
Intelligence (you may believe everything you hear, and never read, and have no idea what healthy really is)
Exposure (they may have never heard of vegetarians, factory farming, or thought nuts were for squirrels.
Anyway, I can't explain the backwardness of human beings.