Stereotypes about sexuality is so vague that it's not easy to formulate a stereotype. However, the majority of Linux/Mac users fit the stereotype of annoying. (Just look at Digg for the example.)
As to the first part, does that stop people from doing it and condemning us all for what they come up with based on the few they see.
As for the second, you're generating it based on a few. I'm a linux user, I've never used Digg, not once. I'm sure I'm not the only one. There's plenty of annoying windows users too, and annoying windows fanboys. But there are a lot of good people who use all different types of OS's, it doesn't matter to me. Sure, I'd love it if you switched to linux, I think it's better. But you may not, and I won't shove my opinions down someone's throat without good reason.
What you say about linux/mac users you can say about any niche groups. Firefox users, Opera users, military personal, religious fanatics, ad infinitum.