The abstract answer: Legally enforceable protection for private property turns out to have some significant benefits for a society. It helps society develop past the warlord stage.
The concrete answer: The article gives some ways that the John Deere idea is bad. In particular, a tractor isn't just a thing that I buy. It's a tool, and I need it to work so that I can plant and harvest my crops. This "ownership" question isn't just a matter of me strutting around announcing to the world that I own it. The question is whether I have the right to repair it in order to get it back to work, or whether I have to wait for the authorized person to do the work.
