My best friend was on an egg and dairy vegetarian diet for 10 years and became anemic and had to switch back to being an omnivore (the natural diet of any human being, contrary to the fanatics posting on this blog). Contrary to what one might think, he was very health conscious and was very careful to count calories and to fill all the supposed quotas for vitamin and mineral intake.
I have no doubt that there are some people that can live a healthy life on a vegan or vegetarian diet, but the cult-like fanaticism of most vegans has basically radicalized me to the point that I have flirted with becoming outright anti-vegan, which would entail me speaking out against vegans in the same manner one might a terrorist group and even recommend forceful repercussions against them if they take to openly harassing people over their diet.
The sort of intolerance that you are experiencing from these people is a reflection of their arrogant sense of arbitrary moral superiority, and in my experience the only thing that has ever caused them to back off is a nice, old fashioned fist to the face.
“My attitude toward progress has passed from antagonism to boredom. I have long ceased to argue with people who prefer Thursday to Wednesday because it is Thursday.” - G.K. Chesterton