Gay Marriage, why it is moral for Christians to protect this interest

I know we have gone over this before, but given that some may not be clear on what is a critical issue I think it may be worth posting on this, since it has been the subject of lots of threadjacks.

Many here have pointed out that it is acceptable to ban gay marriage on moral grounds because all law is based on some morality.  I disagree.

I am a positivist as far as the law is concerned.  We arbitrarily make laws for all kinds of reasons.  Most of these involve giving some economic or political advantage to one group over another.  The law is a tool in the general competition in values. Its doesn’t have a lot to do with morality to favor the meat industry over the corn industry, for example.

However, morality and fairness come into play when we apply laws and infringe on critical human interests, and this is one of the bedrock moral foundations of American law.  Laws should be fair and just when they protect and disadvantage interests.  When it comes to critical human interests, privacy, expression, religion, liberty the law protects these against infringement by the majority.