I think people would be willing to give voluntarily if they receive a service they need instead (as people are now paying e.g. for insurance, or property protection to certain commercial entities).

Will there be enough people to volunteer to pay for nature reserves? Who will pay to enforce a punishment for the enslavement or murder of a possessionless individual with no family? What happens if you need a service like police or a fire department but don't have the money to pay for it? Let them burn your house and rape your family then or what?

The real question is would people voluntarily pay regular fees and would those fees be enough to support those service providers.

You keep citing steemit as if it is an absolutely free market with no regulation while it is not the case. Are not all the hardforks still a form of influencing, regulating and governing the system? I maintain they are and keeping in mind how large some of the whales are (including the founders and the steemit organization if I understand things correctly), it's hard to call it truly decentralized in a practical way.

You are indeed a government system without taxes, but that could not function without regulation either. Would the judicial service provider not be regulated? Who will pay the salaries of the people that help regulate it? Who would decide who those people are? Who would ensure the safety and reliability of that process? Who would pay for all of that? Voluntary fees?

What makes the difference between legislation and protection racket then?

There doesn't need to be a huge difference for it to be the only practical way to organize that we have for now. But the difference is in the intent and process - democracy with the intent to be just vs the pursuit of self-interest without any regard for others.