If taxes are theft, so is property.
Claims to property are secured by force, by the state. Your claim initiates force. As a democracy, we secure these claims under civil law. As a private gang, you secure those claims with your private military.
You take from the commons, expect others to respect your claims, that's theft. However, we agree to recognize each others' claims and live in civil society. As citizenship is voluntary, we agree to abide by the laws of the nation and allow for private ownership.
We agree to pay taxes on income or anything else our elected legislatures tell us to pay. "Theft" is illegal taking, taxes are not.