Libertarianism is a political and moral philosophy based on what we call the "non-aggression principle" or the NAP, as we will refer to it from here on out. The NAP states that No person or group of persons may enact force against anyone else, their property, or infringe on their rights. That seems like a normal thing in the modern day at first glance, but let's look at the implications in politics. Taxation, being forced payment at the threat of force, is a violation of the NAP. In the libertarian eyes it is theft and extortion, and makes the government no better than a territorial street racket, taking protection money from the peaceful people at the threat of a gun. If you choose not to pay, men with guns (called police) raid your house and kidnap you and throw you into a cage. So, according to the NAP, the government is an illegimate organization, as it acts with a monopoly of force that it can use.