I believe you are mischaracterizing the position of a lot of libertarians. While some are of a libertine bent as you describe, many others simply accept that the government has no effective ability to police a lot of actions which come down to individual morals (as in things which don’t harm others), and to even make the effort leads to unintended consequences which are worse than the initial problem.
The drug war is a pretty clear example of this. You don’t find a lot of libertarians who tell you using drugs is a good thing, but they realize the cost and erosion of liberties which has come about because of the prohibition effort is far worse than some people using drugs.
A law doesn't have to be easily enforceable to effectively say, "society says this is wrong." Such a statement goes a long way toward compartmentalizing and rending the practice of such anti-social behavior to an insignificant sub-culture.