[oh_sigh]

Then there would be no general purpose discussions like there are on facebook, only discussions specific to the group that is allowed access. If you only let white people on a web site, it is going to become about white supremacy. If you only let women on a website, it is going to be about womens issues, etc.

[jimmyfw]

Correction: if you only let white people on a web site, then the members on that site will discuss anything they want to discuss (which certainly includes many many more topics aside from white supremacy), but the discussion will take place from the perspective of white culture and white values. There will be a greater chance of deeming other cultures irrelevant to the discussion or (most commonly) simply forgetting that these other cultures don't exist.

With that in mind, you have a logical hole in your statement "If you only let women on a website, it is going to be about womens issues, etc". Women.com will be about women's issues because it is currently being marketed to the general public as a place for women to discuss women's issues. It will not be about women's issues solely because women are allowed on the site. Women who aren't interested in what other women think about women's issues won't find this site very interesting. In general, women will discuss what they want to, where they want.