I see mere property rights as unjust, as they vastly privilege those who were born earlier and those who have through whatever means accumulated a lot of property. That's why I believe we have to have mechanisms to make the distribution of property (or wealth or capital, however you want to call it) more equal. I also think we need to work to create equal opportunities that the market mechanism are unable to provide.
I agree on the constitution, it was written to preserve the property rights of some of the American elites against their competition of some other American elites and English Colonial Interests. That is the case both for Southern Slave holders and Northern Merchants and Industrialists. It is a document designed to protect these elites from losing their status and from ensuring that those who do not have property, and the children of those that do not have property, do not threaten the interests of the ruling elite and their property.
All human interaction is in some way force. Force is a reality of human life, and we should decide which types of force we accept and which ones we do not accept, and what mechanisms we have to ensure that our values are preserved. I assume you are a proponent of the non-aggression principle? That is one way to decide which force you see as justified and which not, and that can certainly be part of a more complex set of rules that govern the forces guiding human life.
I don't see a "free market" as free of coercion. If all public land has been privatized, if your only option for survival is to sell your labor, that is not a free choice, that is a form of force, a form of coercion. If you want to get closer to a free market you should develop something that gives people similar amounts of bargaining power, that puts them in positions where they can really assert their own free will, rather than having a fake choice between doing what the more powerful actor demands or suffering immense consequences like starvation and death.