I think its the extreme. The idea of reducing meat consumption over eliminating it is not met kindly by many vegans and vegan communities. I also see a lot of down play of the nutrient challenge discussion. Now like anything on the internet the extremes tend to be the most vocal. I have personally known vegans who are pretty happy if people are even reducing meat consumption at all or being lacto/ovo pescatarians or such. Its really bad as sometimes the message is if your not going to go full on vegan than your personally responsible for destroying the planet (much like all responsibility for palastinian suffer is because joe bidens the one doing the genocidin) and you might as well eat meat at every meal. The reaction of this for non vegans is very often F these folks and you know what I think I will go out and have a triple bacon cheese burger right now because they taste great.