Again, laws in some states allow it if those involved sign "no-progeny" agreements. And in some they'll allow it with cousins without that. Icky isn't relative to where to draw the line on the government's ability to define religious ceremonies. Victims is where to draw that line.
In similar fashion, I don't really like the way many Muslims treat women. It's not icky like two dudes or incest, but still offensive. But if there is no force used to compel the woman, then the state has no interest in the issue.