In different cultures (e.g. Russia), and different time periods (e.g. the 80's), the level of interest and participation from women is/was much, much higher. I would say that's a pretty objective reason for believing that it's cultural and not biological.

What I find hard to believe is that some people don't think that women get treated differently than men, or that that wouldn't matter when it comes to people choosing to participate in certain communities.