I think it comes down to imagination and confidence. Some people cannot construct scenarios in their mind and analyze their likeliness. And others just want to be accepted and part of the mainstream.

There are also people who simply aren't interested in learning about topics yet feel free to blast their opinions about them. Kind of like how I might say 'country music sucks' when actually there's a lot of good country music but I haven't tried very hard to find the artists I like.