...it's not stealing if you willingly give up something.
For the umpteenth time, I do not willingly pay tax. I pay tax because I don't want to:
a) Go to prison;
b) Leave my friends and family;
c) Live off the work of others.
You can call those 'choices' if you want - same way as if you were mugged at knifepoint in the street, you might 'choose' to give up your wallet to avoid being stabbed. Doesn't make it voluntary, does it?
I think this post is pretty right. There are situations which, strictly speaking, are voluntary. Yet practically, they are not. A 'choice' between jail/death and a wallet isn't much of a choice IMHO' that's coercion.