Humans should actually adjust their diet to reduce global warming and there's nothing wrong in saying that - that's one of the most effective methods of influence.

I'm not a vegetarian, but I live with one and I eat really small amounts of meat now compared to what I used to. I have no issues with that whatsoever, it's often even better and tastier this way, despite of me being a vegetable hater. I really can't see a reason why people so ridiculously defend their meat meals like they're addicted.