Dear Ben,
Socialism is founded on the idea that I can only gain from your labor, if you receive compensation equal to your efforts. (Such as being paid commensurately to what you worked.) Nothing, empowers the worker as much as Socialism. Your Critique should be on Communism and Capitalism.
But I still do net get your point. The common thief does not rationalize that property is unowned. He justifies it, based on that he has needs, and he wants it, and is able to steal. And, that money comes and goes, and repayment is possible.