If you talk to a libertarian, they aren’t for gay marriage, nor are they against it. Same with abortion. They are basically agnostic on those things because they do not think those subjects have any business with government.
Conservatives are different. They know the left thinks they can be in control and make happen(which they have so far) abortion and the definition of marriage. They are always for whatever takes away responsibility and any moral consequence.
The right thing to do is an all out effort to counter the left point of view. I don’t think libertarians really care about those social issues. By accepting them into the fold, they would not be against our opinion, nor would they be for it. Reagan managed to get the three legged stool on board. How did he do it? Of course, abortion is still not repealed, and probably will not be until the culture is ripped away from the left. We gain ground, but it is slow.
If you’re agnostic you can’t be trusted to defend what’s right. Look up “lukewarm.”
Apparently, libertarians have no interest whatsoever in defending the founding principles.