Well, to be fair. In most instances a vegan often goes on about it in a manner which, either intentionally or not, suggests they're morally superior. Now I am not saying that is the case for you and I am not suggesting that we all make fun of people for their diet choices. Maybe I'm old fashioned but I don't really care what someone decides to live off. In most cases I'm judging the individual. Though when your personality becomes 'vegan' then I suppose I have a bit of disdain for them. But that's not exclusive to vegans it expands to everything.
Well then the vegans should learn a lesson that they're not the centre of the universe and the world doesn't revolve around them. They should learn to practice a bit of perspective. Just because vegans see it that way doesn't give them cart blanche to try and force everyone else to see their reality. "What is normal to the spider is chaos to the fly". Life is all about perspective.
Ultimately, and i think it's important to not lose sight of this fact, morals and morality is made up. Not eating meat may align with your moral compass but from my perspective eating meat is a completely normal and natural thing to do. Neither of us are morally righteous over the other in this instance. You may feel that your morals are superior to mine but it doesn't make it a fact.
Humanity will never agree on morals as it can vary from culture to culture so to expect everyone to go vegan cause some people find it horrific... yeah, not going to happen.