I feel bad, because I can't help losing a bit of respect for someone when I find out they are a pc gamer
Why would you lose respect for someone for that?
Because I think those pc gamers are weak
It's wrong to judge people because of their hobbies. You shouldn't judge people for such petty reasons.
I still can't help looking down on them, and I have the right to do that.
This really is something you could overcome if you want to. Try getting to know something about them aside from their gamer status. You might find out there's a lot of other things you like about them.