Its a multitude of reasons for people to go vegan: The animals, their own health, the probability of not creating a living hell on earth. The reason why vegans try to convince others is often because after a few years most are so disconnected from the killing of others for taste where it is a giant argument. The suffering and abuse of 90 billion sentient land animals per year alone is for most good enough to stop supporting it. I have surrendered that argument for most discussions because it is hard to have that empathy while it is a part in your live. It wasn't for me, although is was not challenged in that view back then. So now my arguments moved more towards egoism which sometimes works.