In the various libertarian ideologies there is the idea that only thing that government needs to do is to “notarize” contracts. This is on the first approximation true, but said government needs to somehow derive the authority to do so. That authority comes from government's ability to somehow disperse violence, which in itself requires quite extensive support infrastructure needed for the government to function. And when such infrastructure has to exist anyway, somehow providing access to it for the citizens is a good idea both politically and economically.

Another function of government is, like it or not, in somehow providing legal tender and in the process regulating it. Efficient free markets need fiat medium of exchange, however counterintuitive that might seen. Because otherwise the trading parties would not have any common value reference, and sooner or later the market itself will create something akin to a government and state. Which is well, probably how the idea of governments and states started some thousands of years ago.