re: Why Property Is Theft and Why It Matters

If your starting position is that of common/universal ownership, then the argument in the OP makes sense. The issue is that there is no reason to justify universal ownership instead of non-ownership. In a default non-ownership paradigm (which is what you find in mainline libertarianism), one acquires initial ownership by control/utilization/creation. Once initial ownership is established, ownership is voluntarily conveyed.