People say "social contract". When did we opt in, and can we opt out? It's being enforced without consent. We pay for things we don't want. Whether this be never ending wars around the world, or the welfare state such as the ponzi scheme known as social security.
You are an emergent phenomenon - to claim "ownership" of anything is pure hubris, and reflects a dangerously limited understanding of causality.
Because others contribute to your body's production. Your position only works if you are truly prepared to ask nothing from the state - not defense, not roads, not clean water, not law enforcement. Most people who take the "taxation is theft" position don't recognize how much they benefit from the existence of the state.
You can opt out with the US government as well - it's just a bit more complicated to do so.