Not to put to fine a point on it, but I think it is libertarians that don't understand conservatives. Guess what (as noted in my original comment) all libertarians are conservatives not all conservatives are libertarians. The difference is in policy and executions I suppose. Most libertarians have issue with...well all government while conservatives see it as a necessary evil. What is a law if not the societies desire to enforce an outcome? Usually this comes in the form of a moral, or a value in the case of conservatives anyway. The question is then less about if we should make laws around morality, and more a matter of quality over quantity, and which immoralities we are willing to allow.
While I don't think outlawing sex is even feasable and the kind of sex undertaken gives even less reasoning to forming a law, I do think that restricting sex to private locations is perfectly rational.
This is why I say libertarians are conservatives most of them are more likely to agree in principle with republicans than would liberals, we just often differ in the details. Neither a republican nor a libertarian would have even think about voting for Obamacare. Which one does more damage Obamacare or not being able to smoke pot?