That is absolute poppycock. The true libertarian position would eschew government sanction of any marriage, and leave it a religious ceremony.
Now, what Libertarians are doing, may be a different story. But any rudimentary understanding of basic libertarian philosophy would not allow abortion, child porn, or government license to marry.
LOL, libertarians are not religious and they want anyone and everyone to be able to marry, and you are being silly if you think that marriage law will cease to exist in America, or anywhere else, Thomas Jefferson had a marriage license, George Washington had a legal marriage and paid for his favorite nephew’s license.
“Sexual orientation, preference, gender, or gender identity should have no impact on the government’s treatment of individuals, such as in current marriage, child custody, adoption, immigration or military service laws.”
Abortion:
“ we believe that government should be kept out of the matter, leaving the question to each person for their conscientious consideration.”
And if you want to see the early indications of libertarianism’s position on child porn, just ask.