Why are people on message boards so NASTY?

Honestly, I don't agree that people on message boards are nasty or rude. Yes, there are occasional trolls that post pointless nonsense but they don't bother me because I don't interact with them.
Many people on IMDb seemed to get upset when people don't agree with them about a political view or even a movie. If someone disagrees with you it does not mean they are being 'nasty'. I just means that they have a different view to you and maybe you should grow up if that bothers you.
For example, any time I hear people praising a movie that I don't like, I shut them down instantly. I tell them that they are talking bullshit and I explain why that is the case. If people get offended over my opinion, then that is on them. I have to deal with these babies so often and frankly it's pathetic.
I don't get offended any time someone tells me they don't like Trump. I don't get offended by the idiots that like Harry Potter. Disagreeing is not 'nasty' you sad little snowflakes.