Theft consists of taking a man’s property against his will, regardless of the beneficiary. If the individual has an inalienable right to his own life, liberty and property, then morally his life and property are his to do with as he pleases.
David K. Walter, as quoted in Facets of Liberty: A Libertarian Primer, edited L.K. Samuels, Freeland Press (2009), from chapter 9, “Taxation is Theft”, p. 92.