When setting up a boat detailing and yacht detailing cleaning service business there sure is a lot to know on the topic. I vote for a certain politician based on the promises made during the election. This is an agreement made between me and said politician should they win. I give my taxes to the government rather than have them taken. The services I pay for are part of the promises made by said politician. Should I vote for a politician who doesn't get elected than it is no different than losing a bet. I am still expected to pay taxes. Politics is a gamble where sometimes you win and sometimes you don't.
And since they are, in your mind, necessary, you are entering an implicit contract of paying for them. Through taxes. It is a voluntary contract as well, since if you felt that these things were not necessary, you would be welcome to move to Somalia, where police is non-existant, and so are taxes.
I never said it HAD to be earned. IF it's earned, people stay, IF not, they leave or revolt. It just so happened that the govt formed was good enough for more people to agree than to revolt. Given human nature, most people would "opt out" of many taxes that don't apply directly to them. Unfortunately, the only way a lot of things get done is by taxes that people don't want to pay.
And I'll restate, you can't use the proposition you're trying to prove as one of your premises. It doesn't matter if the government is subject to it's own rules it's still the one giving itself the power to impose unilateral contracts. In fact that's the definition of a unilateral contract.
But monetary transactions are not different than other sorts of transactions, including immaterial transactions, e.g. exchange of information. Your basic statement of morality is consistent with Rights theory, which claims that individuals have a right insofar as it is consistent with everyone else having that same right. In this case, you are asserting a right to not pay taxes that pay for things you disagree with. But this sort of right cannot be universal because the source of disagreement may not be universal principles. Criminals would refuse to pay taxes to support police. Urbanites would refuse to pay taxes to support wilderness preservation or farm subsidies. It would mean an end to taxes and thus an end to government. Insofar as you agree that government is necessary, we cannot have a right to refuse to pay taxes we disagree with, though we certainly have a right to lobby and work to get the laws that impose those taxes and spend them on projects you dislike changed.
You said you want to make government voluntary, that's what makes it voluntary. Nobody here is assuming implicit contracts except for you. Denying the legitimacy of a democratic government because it uses force to enforce obedience is akin to denying the legitimacy of the use of force in self-defense.