The bible doesn't tell us how to set up a government. In fact, the New Testament was written under Imperial Rule of Rome. Much of the prophets were written while much of Israel was in exile and ruled by Babylon and Assyria, etc.
We find them living counter cultural, but not advocating an upheaval of the political system.
In respects to the idea of "normal people" I actually object to that line of thinking. I don't see homosexuals any different than I do any one else. We all have hearts oppossed to God, but they express themselves differently. Homosexuals are not "different" and we are "normal." No we are all sinners, rebelling against God, and desperately in need of His grace and mercy. We are all in the same boat, no matter how that sinful heart is expressed through this or that action.
In respects to how we legislate morality, I agree with your basic assessment. I am having this conversation currently on a Christian website. Here is an excerpt that pertains:
Well, laws reflect morality. I understand the path you are thinking along. And I agree to some extent.
I suppose that the mechanism for determining which moral laws to make legislative laws, are their degree of adverse impact upon society. This has been the general approach at least as far as I can tell.
This is why murder, stealing, etc are illegal. Lying is not illegal, unless it is in circumstances where people are threatened (ie court, contracts, etc).
Drunkenness is only illegal if it is public where it, I suppose, becomes a public detriment to some degree. Which is odd of course because fornication is completely legal, though it adversely affects people to a much larger degree. So its hard to put a definitive grasp on it. I guess it points to fallible people creating laws.
But of course, simply co-opting Israel's laws in the OT would be errant to, since that is a covenant God made specifically with Israel, and was made complete in Christ.
So how do we best approach law making, as Christians, in the 21st century? That is a good question.
and
Well, I am currently undecided about this, but I am flirting with and trying to think through the Ron Paul approach to this matter, which is to get Govt. out of the marriage business. Meaning let Religious and secular institutions "marry" as they see fit. Having it as a social contract as opposed to a Govt. one that has its positive senses to it, but I have not yet thought thoroughly enough through the possible negative consequences, and how deeply that would affect other matters in society and law.