I believe your point is that rights are what society defines them as at any point in history, not unchanging philosophical truths. Is this correct? This seems to be the core question as to what type of organizational system society should follow.
I would argue that the right to your property has always existed. When society has taken property rights away, it was theft then and theft now. Except now it is recognized as such. Not recognizing theft as theft doesn't mean it's not theft. But to your point that I believe you were trying to fish out: I cannot prove this.
Why can't I? Because society has to prioritize the rights of the individual. Limit some rights to protect others. Most obviously, you cannot yell "FIRE" in a theatre. The question is, put simply: at what cost do we protect these individual rights? When is exercising your right at the expense of another's right allowed and when isn't it allowed? The right to life vs property. Do my starving neighbors have the right to life? Isn't that a priority over my right to property? Or do they only have the right to the opportunity of life? Is my owning property directly causing their death? If not, do they have the right to my property to save their life? Or did they give up the right to life by not taking advantage of opportunity?
If I am correct and these rights do exist in reality, then society must answer these very difficult questions. If you are correct and the rights do not actually exist, then we are best served as a slave to society as a whole. But it needs to be organized. And only the emotional man can organize society. With greed and power, the men organizing will inevitably corrupt. So without knowing absolutely who is right between the two of us, where is man better served? A guaranteed slavery? Or freedom potentially at the cost of other freedoms? Look at the best case of both, admit your best case isn't truly possible given the nature of man and proceed from there.