There's such a thing as not having enough information to make an ethical decision, right? We think we know women can't be infected. We think we know, I suppose, that all the men will eventually succumb. We obviously don't really know how best to protect everyone from the other zombies. We're assuming that being a not-zombie and trying to avoid death-by-zombie is better than just being a zombie.
I don't know how much support that last assumption has, really.