You are correct nobody owes anybody any money absent a voluntary and consensual agreement. So why not simply stop giving them money?
Because that's not how our system works.
Our system has the wealthy at the top who preform no actual work, buying into corporations and getting wealthy off the labor of others while they just kick back and rake in profits. As a worker you can't just say "no, I don't feel like giving part of my salary to so hedge fund manager", it doesn't work that way.
These people don't work, they just get paid for moving around money and extracting money from corporations like parasites.
You seem to get in some instances that people don't like to be made to do things against their will. I find it interesting that you don't carry that notion into the idea that some people should have the ability to opt in or opt of a Union arrangement.
That's not really what I have a problem with at all. My problem is allowing corporations to refuse to hire union workers, ending the option of collective bargaining. Right to work does exactly that.