Over in a heated discussion at Free Advice, I am happy to say that Tom Woods has joined in to support my view that "taxation is theft" is a terrible libertarian argument for convincing non-libertarians, because it already assumes a libertarian view of the State, and is therefore circular.
Tom makes an analogy to slavery: Of course, he points out, arguing "slavery is kidnapping" to, say, Aristotle goes nowhere. Aristotle is simply going to respond, "No, kidnapping is taking someone who has the right to be free against their will. But, as I have shown in my writings, slaves do not have that right."
To argue against the pro-slavery person, it does no good to keep saying "Slavery is kidnapping." No, what one must argue is, "These people you treat as slaves, in fact, ought to be treated as freemen." Then you won't even need to make the kidnapping argument; it will be obvious.
And so it goes with "taxation is theft"; that only makes sense after one has already decided (for some other reason) that the State is illegitimate.
Thanks for the support, Tom!