You're allowed to express your opinion but there's no need to be a dick about jfc. You ever heard of the word "ignore"? Especially if you can say that it's not causing problems, then you're literally just going out of your way to say your opinion and be mean about it. And if you're allowed to express your opinion on disagreeing then I can do the exact same thing to you, I'm just glad I'm not an ass about it when I do. And quite frankly you sound like a miserable person to be around if all you do is express your opinion in the most distasteful way. I can't imagine ignoring something you don't like takes more energy then to go out of your way to be mean about it just because you want to.

But if people believe in it then what's the problem? If you don't believe in it cool, but that's like getting upset at a Christian for saying their loved one goes to heaven after they die. I'm not religious myself but I'm not gonna shit on other people's beliefs if in reality it's not hurting anyone. And if people who believe in reincarnation actually believe this is how it works then that's like their "religion". If you don't believe in it then just go away?