Some myths I have heard:

God commanded us to eat animals so therefore it is totally justified nowadays (even if we are breeding and killing and mutilating billions of animals on farms for our taste buds and to keep the fast food industry going, not to feed the starving and poor)

You will be deficient in iron, calcium, D, protein, B, etc (proven them wrong on all these fronts three years later)

Killing animals and eating them to survive is part of the natural life cycle or circle of life or however you want to put it (yeah, and consuming milk meant of calves, eggs meant for birds, farm animals that didn't even exist before humans bred them for food, and I guess it was part of the natural life cycle to mount deer and bear heads on walls and brag about the catch too, and hunt the strongest animal down while leaving behind its children to starve to death, while every other species in the world that eats meat goes after the weakest, therefore ensuring the survival of the species and food source)

People who eat plant based diets are all liberal hippies who live in big cities and have never spent a day in the wilderness

Plant based diets are too restrictive (ha ha if only they knew)