I guess something that seems like just a difference of opinions to one person, someone else may feel very strongly about. Some opinions are considered harmful, dangerous or very insulting by some people and may cause strong negative emotions. After all, any form of discrimination, pro war, pro violence attitudes etc. are often considered just opinions by those who hold them while they are highly damaging to others.
And yes, I've been blocked by people I don't even remember ever having argued with. I assume I wrote something they didn't like at some point but they said nothing. I think it's right. Everyone who wishes to block me for whatever reason should feel free to do so. After all, I wouldn't want to communicate with someone who doesn't want to communicate with me, for whatever reason, and blocking me is a way of letting me know, so I respect it.