Is all online dating just a magnet for mental patients?

I've tried it, and the few people I've met through there, and one I actually had a 7 month relationship with that failed because of his serious mental and emotional issues, makes me wonder: is online dating a place where you have to sift through a LOT of people who have psychological problems? Is there any hope to find someone who's mentally and emotionally stable through there? I simply use it because I no longer go out to places where singles go, all my friends are married now, and it seems easier to meet people that way. But I'm getting very discouraged by my experiences so far.