You may not know many people who regularly smoke pot because you "find it cripples productivity and turns me into a zombie. I stay away from it." You may be seen by users as either hostile, or at least not obviously friendly to their activity, so they self select you out of that information.
I think similarly, people who are anti-gay don't seem to know a lot of gay people, despite the fact that N% of the population are gay.
But in both cases one can choose to let it be known or not. You can choose to share that you smoke or not, and you can choose to share that you're gay or not. It's that choice to share information or not that I'm talking about.
I think similarly, people who are anti-gay don't seem to know a lot of gay people, despite the fact that N% of the population are gay.