Now this is a topic on which libraries of books (literally!) are written so I don't want to get into the details too much.
My reason for writing this post arises from a video I saw of an interview between Rick Warren, the pastor of Saddleback church and a reporter who's name escapes me at the moment. The question that interested me most was the question of whether there is a genetic source to homosexuality or not.
The reporter wondered if science found a 'gay gene' would it change his opinion on the topic. Warren, quite rightly in my opinion, wondered why it mattered. Fundamentally there is a disconnect between what the reporter believes and what the pastor believes beyond simply their disagreement on this topic.
Simply put, the reporter is looking to make a (poor) scientific argument whereas the pastor is making a moral/religious argument. The two are incompatible. It is like two people arguing in two different languages, of course both will come away feeling frustrated and feeling that the other person doesn't understand their viewpoint.
If someone is making a moral argument to you, don't respond by trying to scientifically disprove them because fundamentally you can't. You can't scientifically argue that polygamy is immoral, or that prostitution is not immoral. So don't bother.
An poor way to convince someone who believes that prostitution is immoral to favour legalization and regulation of prostitution would be something along the lines of this:
"Using prostitution is a way to allow people to release stress and pent up hormones. Regular sex has physical and emotional benefits and under the proper conditions we can eliminate STDs and harm to the participants."
Why is this a bad idea? Because someone who believes its immoral will say 'So what? Just because its biologically beneficial doesn't mean its moral. If you want to have sex, get a wife!'
A better argument to use would be something like:
"Regulating prostitution removes women from the typically abusive control of pimps and gangs and can get them into a position where they can receive proper medical attention. Legalization and regulation would make prostitution, which will occur anyways, more safe for prostitutes."
From a moral point of view this is much more difficult to refute than the previous argument.
The same works in reverse, people who think in terms of these issues as moral/religious arguments should tailor their arguments towards their audience and use scientific arguments rather than moral/religious arguments against or in favour of their causes.
This is a rather universal principle I would think, but I'm still surprised to see some people don't get it.