**I have libertarian leanings, I think the government should be very limited, and that it is a social construct to protect physical things, like life and property, and should have their hands off of spiritual, philosophical, or intellectual things. **
Since the government has is a reasonable responsibility to protect people from harm, there are laws that regulate something like the use of certain drugs etc.
I would argue that if drug use only harms the person using the drug, it should be legal.
If there is solid evidence that drug use actually cause harm, or the potential of harm, to others, then the government should regulate those drugs.
Take alcohol. Alcohol is a drug, a perfectly legal drug in most circumstances, unless you are operating a motor vehicle. In that instance, you are a danger to other people. The government has the responsibility to protect other people, therefore, they have the right to regulate the use of driving while intoxicated.
If somehow there were some study that produced some data that same sex marriage causes some harm to society, the government has a reasonable responsibility to regulate it, otherwise government is only protecting the property rights of two people that signed a contract, which I think is pretty reasonable, even if I disagree with the sexual morality of the two people participating.