It's not theft if you give your consent. Which you do every time you sign a government form (contract). It involves a legal tactic the tech sector has made great use of, "default opt-in". That's not it's legal name, but it conveys the idea. Legally their just contracts, think "terms and conditions". But, just like with "shrink wrap contracts" and "click wrap contracts" in the tech world where presumptions are made under the law, presumptions are also made about your citizenship. Most people are completely unaware that there is both federal citizenship and state citizenship.
"There is a distinction between citizenship of the United States and citizenship of a particular state, and a person may be the former without being the latter." [Alla v. Kornfeld, 84 F.Supp. 823] [(1949)]
And as some are aware congress has unlimited authority to legislate within Federal jurisdiction, but must abide by the Constitution in the 50 states.
Explore here for more info: (pdf) http://sedm.org/Forms/10-Emancipation/CitizenshipDiagrams.pdf
RE: Why taxation is theft