alt Hacker NewsYou are perhaps confusing libertarians with anarcho-capitalists. Ancaps are a subset of libertarians. I think among other right-wing libertarian varieties there is a broader spectrum of beliefs, and left-wing libertarians generally would not support anything that pollutes the commons (although they would disagree about the best means of preventing such pollution).
Left libertarians, while they exist, are definitely a minority opinion.
But I'd say that they also don't have a good solution to this problem as it requires more centralized enforcement to really make a difference. A tribal council shunning the polluter or even ejecting them from the community isn't likely to result in them stopping their behavior. Not unless a huge portion of the world adopts that government (which is unlikely).