Voluntaryism is based on the idea that you don't own other people, in whole or in part.
Axiomatically (see Rothbard, Rand, etc.) you own yourself. This implies several things:
* you own your labor, and may trade for it as you wish, and nobody has any right to interfere with such trade, or to take any part of it (as "tax" or otherwise); * you have a right to your life, that is, not to be killed or harmed if you do no harm; * you have a right to liberty; * you have a right to property obtained through homsteading or voluntary trade.
These rights also imply the NonAggressionPrinciple.