> But that doesn't mean you couldn't a) pare back the state to the bare minimum functionality (which doesn't include garbage collection, IMO) and fund it voluntarily.

You could do that with the entity called “the state”, but that entity would no longer be the state or government, no matter what it was called. (It might be an arm of the real government, which might consist of entities voluntarily funding the “state” which themselves exercise coercive, in practice, extraction of wealth, or it might be an irrelevant figurehead.)