Sadly, while self avowed Libertarians may be fringe, some of the more demented and intellectually stunted aspects of their ethos have taken hold in mainstream Republican Politik. Libertarianism can't be mainstream because it literally doesn't work in practice. The actual mechanics of it don't map to reality. But Libertarianism's ideals are aspirational for half of our political culture's mainstream then there is plenty of damage to be done. We've been seeing this for years now. It's horrendous.Libertarians are fringe
Although I think you can easily find instances of people practicing 'libertarian principles' (and probably just as easily 'communist principles'), IMHO there is a great distance between that and a successful public policy. The reason why I also mention communism is that I find libertarianism and communism to be very similar in the fact that they don't naturally occur on large scales, which I think is very telling.