There is no such thing as "bad ideas", only ideas that you personally reject. This is true about Islam, about far-right ideas, etc.
So you are a libertarian? Then it means you personally reject anti-libertarian ideas, that you call "bad ideas we must legitimately fight". And you probably also oppose voluntarily enrollment into slavery, voluntarily enrollment into a deadly manhunt reality show, voluntarily selling your arm to a cannibal butchery, etc. All things compatible with libertarianism but that you reject. Simply because you do not like those things. Because you want *your* values, your peculiar version of American "libertarianism", to prevail. This is fine, this is human, just stop pretending you do so because of some universal laws revealed by libertarianism's founding fathers, that all humanity must follow.
So please stop trying to make the whole world like the USA. Stop pretending the American libertarianism is the one true dogma that all will eventually converge to, and the only legitimate policy. The world is better when it is full of diverse civilizations with diverse values, cultures, languages and laws. Which is only possible by rejecting opposite ideas, and there is nothing wrong with that. For example I do not want a Franco-Islamic France. By the way, being allowed to stand for what *you* want for your country is called democracy.