«Nozick claims that a requirement to pay taxes is on a par with slavery»

In most countries there is no «requirement to pay taxes», paying taxes is a totally voluntary option: for example I don’t pay the high taxes of Sweden by the simple device of not going to live in Sweden. There is a market in levels of taxations and people can purchase the citizenship of the country that best suits their level of taxation preference.

«Most people cannot purchase citizenship of any country»

For a proper libertarian that kind of “positive” liberty does not matter: for a libertarian if you could have the surgery that saves your life but can’t afford it, that’s your problem not the collective problem of ensuring that you have the freedom to have such surgery if you can afford it. If the jackbooted thugs of the government do not prevent you from choosing something else, then you are free, regardless of whether you can afford to choose something else.

People who don’t understand the structure of libertarian argument can be misled by the clever dissembling they are usually based on.