Okay, this is going to get a little rant-y.
Let me begin by saying that I am a vegetarian who eats vegan most of the time. I believe it is healthier and better for the environment, and eating animals made me sad when I was an omnivore. That being said, I am getting really sick of the self-righteous vitriol that some of my plant-based brethren are spouting.
Listen, we have the luxury of being picky about our food in this country. Not to say we don't have hunger problems here, of course we do. But hunger is not a reality for most of us. We get to develop ideologies about our diets. Make statements with them. Obtaining food is not a matter of survival for most of us, eating is something we do for pleasure.
Simply put, no matter how much you might think a vegetarian or vegan diet is something the whole world should adopt, it is not a possibility for everyone. A vegetarian or vegan diet is not something that is sustainable everywhere. At the very least not possible everywhere right now. I feel lucky because I have the luxury of not eating meat. By that I mean plant-based alternatives are readily available to me. I have the luxury of turning down food. "No thank you, I'm a vegetarian." There are areas of the world where the kind of large-scale agriculture needed to sustain the population on plant-based food is not possible, and trucking or flying in that amount of produce would result in worse pollution. Western China, for example. Not all Tibetan Buddhists are vegetarian. In Tibet, and Xinjiang, in the Gobi Desert, growing that many plants is simply not possible, and so in those areas diets are overwhelmingly meat-based. When I lived there I had to relax my standards. I ate tofu soup in meat broths, I ate vegetables that had been roasted in pots with meat, picking bits of meat off them, I drank tea flavored with sheep tail fat. I'm sure I unknowingly ate things, it's an occupational hazard as an anthropologist. I did these things because that was my option. That, or not eat. And I was only there for several months. If I moved there permanently, I would have to go back to an omnivorous diet.
I do not consider it a moral failing on my part that I was not a strict vegetarian while I was there. I do not consider it a moral failing on the part of the locals that they eat mostly meat. I don't think the Dalai Lama is a bad person because he only eats vegetarian every other meal. I don't think not eating meat makes me a better person than those who eat meat.
The bottom line is insisting that everyone live like you live when they do not have your opportunities or access to the same resources you have, and then calling them bad people if they don't, is arrogant and myopic. You want to try to convince your fellow Americans to convert to a plant-based diet? That's awesome, go for it(in a positive manner, calling them murderers is just alienating and makes us all look bad), but please please please stop crusading against the evil meat-eating populations of countries whose climate and agriculture you know nothing about.