Right, but the existence of disagreement does not mean there's no means to determine the truth.
The line between the two is a bit fuzzy, you have to admit. In the case of economics, a lot of "observation" relies on interpretation of the data, which is subject to error.
You're conflating two aspects of that issue though. Why people see the need for property is not precisely the same question as to why property turned out the way it did. That distinction is important. When one has asked the question: "What is property for?" then one can assess the appropriateness of property as it actually is.
We could distinguish between the ethics of property and the history of property (and avoid the use of theory in either case). So, I guess the better question at this point is what do you think about the ethics of property, rather than its history?
No, I'm not saying you're not allowed do that. I'm asking on what basis you think a person is capable of doing so? Pure whim is obviously not your answer, so thus, there are objective criteria involved (however difficult it may be for individual people to reference them).
Ah, but isn't that concept of citizenship itself merely a subjective value judgment? Pure subjectivity always ends up in this sort of problem. I fully concede that humans have difficulty comprehending reality, and I'm not pulling in some obnoxious imaginary friend in the sky to provide me with a level of certainty that I would otherwise lack.
Their disagreement has no bearing on the truth of the matter. I find it hard to construct a consistent ethic of property where slavery is a possibility and I contend that it is probably impossible to do so.
Maybe, maybe not. People do change their minds on issues. The whole process of argument is about changing minds or influencing minds that are not yet made up.