To give an example, many years ago while at uni, I was eating lunch in a canteen with some friends. A group of vegan activists turned up and was going from table to table to discuss people's food choices. They came over to us, it all started very nice, we said what we picked and why, and then it turned pretty nasty. They were overal passive-aggressive/aggressive, the way they spoke to us gave us the feeling like if we were inferior. I didn't disagree with them that eating vegetarian or vegan was a better option, but the way they spoke to us really wanted me to go and order a pepperoni pizza and shove it into my mouth in front of their eyes.
You know when people may even be right, but the way they try to convince you is so forceful and unpleasant and makes you feel like a worse sort of human being.
There are ways to debate things, but I am not sure making other people feel small is the best way to make them agree with you?