Taxes are involuntary

Is that a bad thing?

If the person does not volunteer, then you would be harming the person by forcibly taking the money in the form of a tax

Depends on what you mean by "harm". Forcing someone to do something doesn't necessarily harm them. When my daughter was a baby, I had to force her to take her medicine when she was sick.

Ethical people avoid initiating harm against peaceful people.

Sure, I can believe this idea. But again, it depends on what you mean by "ethical people" and "peaceful people". By my definition, there aren't that many ethical people in the world. Or at least not enough of them to pay enough taxes voluntarily.

The person who gets to define the harm is the intended victim

I disagree. I'd say only ethical people should be allowed to define harm. Otherwise, "harm" is too subjective and it can be whatever.