How does that then lead to trying to dictate what is legal/illegal for non-Christians?
I wish I knew. As a Christian, this is the bit that frustrates the hell out of me. To be fair, it's seem to be largely a problem with right-wing Christianity in your country (assuming you are a US citizen). Over here in the UK, there are a couple of small vocal Christian groups that make some noise about these issues, and get laughed at in the press. The main issue reported over here concerns homosexual priests practising in the Church of England.