Why are people judge mental about people when it comes to renting a room?

Because a lot of people are mental and you don't want one sharing a place with. It's a big deal. It's who they hang out with, who they might invite over, it's whether they get mad over who gets to use the bathroom first and whether they're mental enough to grab a knife and "defend" their right, it's whether they might rob you or do worse while you're asleep etc.

Maybe they are looking for someone to be a friend and hang out with, it’s not judgemental, they just want the right person to share their house.

@AlienWhitePower 🤔precisely it is thought you are being persecuted and stigmatised for this

People will judge just about anyone or anything because they have nothing better to do.