I think that a lot of men are scared by the whole birth thing. They've heard so many stories about pain, blood, fainting, screaming and swearing, "near-death-experiences", and "if-we-hadn't-been-at-the-hospital-they-would-have-died", from who knows where. So they want the two people they love most in the world - wife and baby - to be as safe as they can make them! And what could be safer than the hospital, right?! Wouldn't you have thought that if you hadn't done your own reading and research? I know I did.
Many men are a little bewildered by how a woman's body works at the best of times, let alone during child-birth, and so they want the "professionals" to handle this. And, given the way homebirth and private midwives are generally viewed by the media, it's no wonder that men don't see this as a good option.
So, I think that as the previous posts have said, gentle education is the best option. Show them the failings of the current system, and the options that are out there. Show them the statistics and current research on homebirth. I don't think most of the guys out there are really out to be idiots about birth - they love you and want you to be safe. The thing is to convince them that you are safe, even safer, at home.