You're dying of cancer. How much will you pay doctors / drug company to keep you alive? Is the transaction voluntary?

Think carefully what voluntary means. Many, if not most, people, in their daily lives, don't have much volition.

I don’t think the second bit follows from the first. You’ve cherry picked an example of tough circumstances that most people don’t face.

You don't even need to use such a dire example as cancer to see how wealth would get transferred involuntarily.

Say your neighbour falls on hard times, and instead of just helping him, you offer to buy some of his land, or his watch, or whatever at a disadvantageous price. Or you lend him money at unfavourable terms.

There are real life businesses that operate today, pawn shops, cheque cashing places, that grow wealthy on the poor.

The way to avoid giving what little wealth we have to the man, means to rely on one's community, but in North America that is being eroded more and more.