If you are talking about me, and I suspect that you might be, I ought to put you right - I've never maintained that all property is theft. I do understand the argument though, and have some sympathy for it. Reckon you may well have read this before but others might not have. It was written close to 200 hundred years ago but it's still as relevant as it was then:
"If I were to ask the question: what is slavery? and I should answer in one word, it is murder, my meaning would be understood at once. No extended argument would be required to show that the power to take from a man his thought, his will, his personality, is a power of life and death; and that to enslave a man is to kill him. Why then, to this other question: what is property? may I not likewise answer, it is robbery, without the certainty of being misunderstood?; the second proposition being no other than a transformation of the first?"
Come on then, if you want to talk theory, someone give me a decent answer to Pierre-Joseph Proudhon's very reasonable question....