taxes are needed unless we want a complete anarchy.
This is incorrect. Government could be funded voluntarily. It's not binary between taxes and anarchy.
This will admittedly be an argument of symantics but i dont think this is correct. Tax collection is one of the defining characteristics of government. Any organization that is funded voluntarily is necessarily not a government by virtue of the fact that it is funded voluntarily.
I think the right term for an organization that behaves like a government in other ways but doesnt force people to fund it would be mutual aid society.
If you define government as 'The monopoly on force in a given geographic area, which is funded through involuntary taxation', then you are absolutely correct. More correct would be what you said, or 'The administration of society need not be funded through involuntary taxation.'