MikeT is going to attempt to formulate a case for Christian libertarianism, and since that's a noble endeavor, I figured I'd throw in my 2c:
One major point of Christian libertarianism lies in asserting the difference between morality and the law, and if there’s one legal cornerstone upon which Christianity rests, it’s that the law cannot make one moral. Passing a law does not make an action moral or immoral. One cannot make theft moral by commanding it instead of banning it, nor can one make marriage immoral by banning it or by regulating it (e.g. laws forbidding mixed-race marriages) or an immoral* marriage moral by allowing it. The thing is moral or immoral on its own accord, and while law can (not must, can) flow from morality, “It’s against the law!” is primarily an argument from force, not morality. This is precisely the reason that Jesus spent so much effort pointing out that even those who obeyed even the smallest points of God's law could not claim any moral credit for doing so; they are simply two different things.
A second one is like it: no man can obey the law all the time. Peter says as much in Acts 15, when he answered the question of whether non-Jewish Christians were to follow the Law of Moses with another question: “Why do you tempt God by putting a yoke - which neither our fathers nor we have been able to bear – upon the necks of the disciples?" The answer was that they could not and they therefore did not. Even though the law was good (Rom 7:12) I cannot keep it. The Law of God is not applied to me, not by the church, and certainly not by a majority vote of other people, for with a law that I cannot obey comes a condemnation I cannot avoid.
But what about the people it was originally applied to, the people who promised to keep all of God’s law? They could not, of course, and many of them didn’t even try. But there’s a funny example that a lot of Christians use, for example, to make divorce more difficult. When the Pharisees asked Jesus why Moses allowed them to divorce their wives simply by writing a “Dear Jane” letter, he replied, “Because of the hardness of your hearts Moses allowed you to put away your wives, but from the beginning it was not this way” (Matt 19:8). Jesus called his disciples and his society to a higher moral standard than was found in the law, but that is not the only issue, nor even the main issue, when it comes to writing law.
The main issue is that God adjusted the law to how Man really was, not how he wanted them to be. God knew that a law that made divorce impossible would make life miserable (mostly for wives) and so he chose to allow the Israelites a lesser evil than marital misery: divorce. What God joined, God allowed to be separated because Man simply cannot live up to God’s standards. Jesus did not propose that Jewish society repeal what Moses gave them, he proposed that they individually live to a higher standard, that they choose to be more moral than the extant civil law commanded.
When Christians propose laws that make divorce more difficult than God made it, we are saying that our expectations of mankind are higher than God’s. We are saying, in fact, that we are holier than God says we are and that we can use the power of force in a way that God was unwilling to do to make people holier than God expected. In finding God’s revealed rules for civil living too loose, we are saying that we know better than God how Mankind will act in real life. That is a dangerous thing for a Christian to say.
But that all only applies in the negative, the passing of laws to forbid and condemn behavior. Is the case for the Christian libertarian based primarily on that? Of course not. The separation of law from morality is simply a necessary step in denying one of the foundations of modern political ideology: that what one person finds immoral, no one else ought to be able to do so long as one can whip up a majority to go along.
That idea is so foundational that it is seldom questioned, and while it is not limited to Christians by any means, Christians are most likely to put the argument in explicitly moral terms. We would ban prostitution for any number of named reasons, but the primary one is doubtless that we find the visiting of prostitutes to be immoral**.
We ban drug use for the same reason: we personally disapprove of the practice. Or more exactly, we disapprove of OTHER people taking part in the practice. People do not generally take part in practices that they find immoral, or when they do, they hide the fact rather than try to pass laws that will use the force of government to stop them from doing it.
But in addition to the call for the Christian to seek a higher morality no matter what the law says, there is another very important idea, a different standard, in the New Testament. That standard is one of individual liberty. After telling the Romans in Chapter 13 that love is the fulfillment of the law, Paul introduces another standard: “Let every man be fully persuaded in his own mind.” Whether it is eating meat or drinking wine or observing holy days***, Paul says, in essence, that what another person does is none of your business. "Who are you," he asks, “to judge another man’s servant? To his own master he stands or falls, but he shall be held up because God is able to make him stand.”
What, in fact, Christianity calls for is the internal discipline of morality rather than the external discipline of civil law.
[End Part I, because I have a Spanish test Thursday, and I’m having a heck of a time conjugating a couple of particularly troublesome verbs. And besides, I’m not going to do all of Mike’s work].
* “immoral marriage” is probably an oxymoron. It might be better to say that which is not a marriage but is pretending to be one.
** Which it is for any number of reasons. None of this is designed to convince the Christian that his morality is wrong – i.e. that he should begin to do these things - only that he is incorrect in imposing the finer points of his morality by law.
*** See Commandment IV.