how does gay marriage lead to polygamy?

While we’re at it, I would mention that the law passed last year in Spain and allowing both mariage and adoption for homosexuals will come into force tommorrow.

If I’m not mistaken, Spain hence will be the third european country to allow same-sex marriage, after the Netherlands and Belgium.

I don’t think so. If I understand correctly, the spouse can request an annulment in this situation. But people aren’t prevented from marrying on the basis that they don’t intend to have sex. Espcially not, I would assume, if none complain about it.
For instance, would a man who’s been acidentally castrated (or who can’t have sex for whatever other reason) be unable to marry a woman?

My comment was in response to a post stating that the governement must be involved in marriages because, amongst other things, parental right issues have to be regulated by the law. I was only pointing out that parental rights are already regulated by law and handled by courts even when the parents aren’t married.