Yeah, I'm gonna have to sharply disagree with that. Ultimately all people own themselves. Even a slave chooses to be in the relationship, and chooses not to end it even when they're unhappy.

The only real difference has to do with to what extent the sub-or-slave can say "no" to one thing without saying "no" to the entire relationship. But even on that scale there's no sharp line with subs on one side and slaves on the other.

It really comes down to just a matter of personal style. Some people like the "feel" of ownership and slavery, some don't. And that preference is only loosely correlated with things like depth of submission.