Many libertarians believe that taxation is theft because they believe that their money is their property. Let’s say that you hit a libertarian over the head and take his kidney. He would consider it to be theft because he perceives the kidney to be his property.
Let’s change the scenario. Rather than you taking his kidney… the libertarian sells it the day before on the black market for $5,000 dollars. You hit him over the head and take his money. He would consider it to be theft because he perceives the money to represent his kidney.
However, nearly every libertarian who makes the theft argument against taxes really isn’t making an economic argument… they are making a moral argument. Their property is sacred and any effort to confiscate any of it is unethical.
Libertarians who rely on moral arguments only do so because they are largely clueless about the economic arguments for liberty.
I used to be a libertarian but now I’m a pragmatarian. I’ve had a few pretty useless debates with moral libertarians. In one memorable debate… the moral libertarian argued that choosing where your taxes go is like choosing your rapist. Eh? If I could choose my rapist… then I’d choose somebody who I’d voluntarily have sex with… and it wouldn’t be rape.