Yep, that idiotic liberal relative, stupidly leftwing friend or nonsensically "progressive" co-worker.

Okay, you're correct to notice that leftism does dominate the group you cite. But it regrettably can be found everywhere.

For example, black America is as wildly liberal/leftwing as the sub-group you single out. So are GLBTers.

So are the many people in Beijing, the EU, South Africa, Venezuela, Mexico, Canada, etc.

Liberalism is a nasty dynamic that knows no boundaries.