How do you know these folks are liberals? Have you asked them?
Tiburon is pretty high end, and as such probably has fewer
socialists and hippies than the rest of Marin.
I wouldn't want a bunch of the unwashed in my neighborhood either. The cars on the lawn and graffiti would be unsightly.
My general perception of high-end places is fiscally conservative, socially liberal (and thus more libertarian than liberal), and extremely protective of their community lifestyle, i.e. NIMBY-minded.
But NIMBY issues rarely come to high-end communities because the land is so pricey - just about any undesirable development that would offend NIMBYs could be more cheaply and more easily pursued somewhere else.