Personally I don't even have a problem with having marriage defined as between a man and a woman at the state level, but
1) I think that it's important for Rand to take a consistent position on the issue and stick to it.
2) I'm afraid my position on the issue has become so unpopular that it might be impossible to win a general election while taking that position. The marriage privatization position would appeal to more people in a general election. But, if he takes the position that the states should define marriage as between a man and a woman in the GOP primary, and then in the general takes the position that there should be no government involvement in marriage even at the state level, he could be accused of flip flopping. That's what I'm concerned about.