Sex with Aunt Flo

I wanted to alert everyone to this very interesting discussion on Aysha's blog about Islam, polygamy, and sex during a woman's period. This is actually a topic that's come up several times recently in conversations with my friends, and the opinions ranged from "it's better during my period" to "it's gross and ain't happening." The most frequent response was "I'm fine with it, but if the guy is grossed out I understand," which I interpret as leaving one's partner free to decline sex for any reason, at any time. I think that's a bare minimum threshold for an honest and respectful relationship.
What I find more interesting (and, as a feminist, more disturbing) is the near-universal link between the female reproductive functions and dirtiness. I don't dispute that menses or childbirth are messy, but why the negative connotations and prohibitions against visiting religious sites, having sex, praying, or interacting with men? There are all sorts of norms like that in Christian, Jewish, Muslim, Native American and surely other traditions. If the reasoning is that women need rest and to be exempt from other obligations during the "womanly times," that's one thing - and I wish American society would respect that more and that lengthy maternity leave was more common. But there's a big difference between giving women the right to rest and to be left alone and prohibiting them from engaging in their lives and communities. It's the difference between an egalitarian society where women are free to determine their needs and how to meet them and a patriarchal ones where women are precious chattel under the benevolent protection of men.