Government isn't defined, by function what would be defined as the government in the context of agorism, what would it do/service?
BTW, would it surprise you to know that government defines taxes as voluntary and taxes legally are there because of using certain benefits, the maxims of law that deal with Benefits enunciate that since time immemorial: http://www.ecclesia.org/truth/maxims.html#Benefits.
Agorism is a process of replacing government functions by ignoring the government option as much as possible and seeking free market alternatives. Ultimately, this results in no government.
I generally define government as an institution claiming and generally exercising the prerogative to tax, seize through eminent domain or civil asset forfeiture, and conscript.
I don't believe government is necessary at all.
Anything currently handled by government institutions can be handled better by the free market, including security and arbitration, even punishment if we manage a shift in mass opinion from expecting government to punish those who need punished to realizing it need to be done by the community directly. For example, a private arbitration service could determine that someone is guilty of murder. Instead of expecting a government entity to handle this, the community should execute him directly.