hope that someone else will merit you for this beautiful analogy).
Another aphorism with regard to taxation that I really like:
"If stealing 100% of the working power of someone is called slavery...
at what percentage does it stop being slavery?".
The main difference between slavery and contribution is the choice. As long as you can choose how much you want to give it's not slavery. If the contribution is forced upon you it usually means slavery because you're working for the benefit of others.
Taxes are slavery despite the amount because if you don't pay up you'll eventually get locked up. To simplify they are willing to take away your rights for not working for them.
In fact, that remains to be seen. For example, when you steal from somebody, they can demand you pay back what you took. Would you call that slavery too? Well, I think regular thieves may certainly do, but we all understand (I hope) that this is not the case. But taxes are like that, at least they claim to be them like that. Basically, with taxes you pay back what you have taken or consumed as public good.