the state is a territorial monopolist on ultimate decision making and taxation, it is not the result of any kind of legitimate contract and even if it were no one would sign such an outlandish thing. the state sets the price you must pay for it to protect you or do any "good" thing that you may believe it does while ignoring the bad that it must do to achieve. it does this regardless of if it even succeeds in doing what it is supposed to do.
Taxation is the compulsory and involuntary expropriation of property from one individual another person or group.
it is theft regardless of 'pragmatics' imaginary contracts, or whatever other non argument you wish to you.
For anything to be 'theft' you need to have a concept of ownership in the first place. You seem to want a concept of ownership that exists independent of our current society, but this is unsustainable. Ownership must be defined by the society in which we presently exist. Anyone can claim to own anything they like but there has to be a single entity which makes the ultimate decision on whose claims are true. That is a monopoly, it is true, but nothing else would be remotely practical.