I have no issues with veganism but I do have issues with being attacked because I'm not vegan. I've been attacked for using cow milk even after explaining that I can't use plant milk because of sensory issues.
Funnily enough, just like you said, I know vegans IRL who would never behave that way and of course I accommodate their dietary choices when I'm in charge of food.
I think it's mostly an Internet thing when you just see the loudest minority instead of the more quiet majority.