How? In a libertarian society, there are no social costs as there are no socialist programs designed to keep people with a self destructive lifestyle alive.
What seems to be upsetting you is the fact that people out there might be doing things you don't approve of. Tough. Deal with it. There are people out there doing things I'm fairly certain I don't approve of. It isn't any of my business. If they try to initiate force/fraud/theft agaisnt me or mine, then I'll kill them. It's what we have a Second Amendment for.
Pretty soon, you'd run out of Hippy wanna-be's through sheer attrition and the species would excise that self destructive trait from the gene pool. This is a good thing.
Time to stop standing in Darwin's way.
Yes, under libertarian politics you can have a whore in one land legally and your grandpa dying in the streets in front of your house in front of the kids next door.