@simcha613 – That is not entirely true. It is not purely a moral issue. It can be argued that it is no different than the government commanding people to wear a seatbelt or not do drugs. Why should they be concerned with what I do? The answer that is given is that it will be a drag on the rest of society if you crash have higher hospital bills, etc. The same argument can be made for these couples. The rates of many diseases are significantly higher than in other people. LGBT have way higher rates of depression and suicide. Much higher likelihood of being homeless. These can be a major drag on society. (higher medical costs and the like).
Basically, its a much easier argument than forcing you to put on a seat belt.