Let's say the US retaliates against Iran's threat of force (let's just assume it makes a legitimate threat of force) and kills uninvolved Iranian citizens as a side-effect. Assume the US made reasonable attempts to minimize civilian casualties.
Was the US's force against those civilians retaliatory, or initiatory? I would say the former. Iran initiated the force and is morally culpable for those deaths.
If you agree with me here, we can procede. But this is important. I am saying that when the US (for example; imagine, now, that it is a mininal government) levies taxes to establish basic, necessary protection of rights (minimal police, courts, and military), it is analogous. It is retaliatory. The threat of initiated force being retaliated against is robbers, theives, foreign countries that would invade, etc. We know all these will run rampant without government (at least you can agree with me that that is true given the way society is now). It doens't have to be a specific thief or other rights-violator; we know they are out there, and that government is necessary to protect rights.
So when an ideal US forcibly taxes me, it is retaliating, for the same reason it is retaliating when there is a civilian casualty in Iran.
Anyway, we run the risk here of being rationalistic (i.e. talking all about concepts that ultimately are not connected to reality). There is another way to look at the point that I am making, which is to say: In a state of nature (i.e. if the government suddenly disappeared), force rules. The only way to get out of a state of nature is to use force to elimiate it. That is perfectly moral, and perfeclty practical. It is the use of force that makes the protection of rights possibile. (That would even still be true if government were 100% funded via donations, since it properly uses force against criminals anyway.)
> You cannot justify the claim that taxation is immoral
You said it is immoral "plan and simple" because it's "extortion." Unless I missed your argument. That does not justify the claim of "immoral" because it does not link it to a philosophical theory of morality that itself is, ultimately, logically derived from and necessitated by perceptual reality.
For instance, many libertarians support the "nonaggression axiom." That is just a floating axiom that they arbitrarily assume. Some of them have deeper philosophical arguments for it, presumably, but many do not believe that such are necessary.
The good news it that we actually can rigorously defend liberty using a chain of reasoning that starts from perceptual reality. And we should. Don't be satisfied to believe a good thing when you can also prove a good thing, which is so much better. :)
However, that reasoning will lead to the conclusion that a minimum necessary amount of taxation is, well, necessary, and thus justified. A proper theory of morality does not contradict that. I am willing to sacrifice the ideal of having zero taxes in exchange for being right.