You don’t have to be socially liberal to be a libertarian. I’m pro-life and a Christian, and a libertarian. I believe abortion should be banned like all other forms of murder, and I believe the government shouldn’t be involved in marriage.
You can be Ted Kennedy and be personally opposed to abortion, but if you promote and support and defend libertarianism then you are promoting, supporting and defending their social liberal war against social conservatism and their efforts to drive it out of politics.