Honestly, I can't speak for everyone but I think that any person (or fan if you will) who is deeply passionate about something may come off as 'intense'. I mean, there are stans everywhere you look whether it be western or eastern or w/e kind of music. It's just how it is
.
Me personally, I just try to ignore it when people put down my favorite music/artists because
everyone is entitled to his/her opinion & whether he/she likes it or not has nothing to do with me.
Of course, there is a fine line between just pure opinion & bashing (where it just gets disrespectful), but even then what's the point of letting it get to you? Chances are the person bashing the singer/artist has no idea what he/she is talking about & aren't even worth your time of the day lol, so really...there's no point in letting every little negative thing get to you (I mean 'you' as in everyone in general btw).
So yeah, in a nutshell you're gonna see this kind of thing everywhere you look...it's not exclusive to k-pop fans by any means.