Why do people feel the need to shame other people's choices in order to validate their point?

I can understand it in some cases. Like.... People who oppose abortion often genuinely believe it is murder. If I believed babies were being murdered, I'd speak up, even if it was getting into someone else's business. And a lot of vegans genuinely believe animals are being treated with cruelty and abused (which is actually true with major production). But they think killing animals at all is heartless, so I understand them speaking up. But I'm VERY much so, "if you don't like it, don't do it" with such cases, and I myself try to buy from smaller producers with things like meat to avoid any unnecessary cruelty (I think the MEAT industry should be reformed, not necessarily people's diets to avoid cruelty). So I do get, to an extent, why they're loud with their protests. What I don't get is the common hatred and disrespect to those who disagree. Like... Screaming at someone, calling them names, belittling them, making them seem inferior... That's NOT going to get them on your side, so what's the point lol?