The validity of treaties signed under duress on the other hand I think really deserves some questioning.
Historically, a huge number of treaties have been signed under some degree of duress – most peace treaties are only made when one side is clearly winning, but extracting concessions (however painful) from the losing side is more in the winning side's interests than the risk and expense (in blood and treasure) of continuing the war to a complete military victory.
If one took seriously the idea that treaties signed under duress are invalid, the national borders of Europe and North America (among other places) would have to be very different.
An entire world war was fought as a direct consequence of one said peace treaty. Nazis wouldn't have been able to gather that much support if the Treaty of Versailles hadn't been specifically designed to aggravate the germans.
If torturing you into selling your assets makes the transaction worth questioning, why would we not question it when whole countries do this to each other?
The problem with "questioning transactions" is that if you happen to own any real estate, almost certainly it is land which was stolen from somebody at some point (from indigenous people, or by some invading army, or by some greedy feudal warlord, or whatever). You want to open that can of worms for other people, but do you want to open it for yourself?
So, here's the issue. In other countries, especially over here in South America, this kinds of transactions are heavily frowned upon, and criminal acts resulting in a sale are regularly cited as reasons for voiding some sale or another. This is a bit of a worldview issue, we're not used to thinking about inflicting misery on others as a legit business strategy.
Wherever you are in South America, isn't it the same story? The Europeans (the Spanish or Portuguese or whoever) moved in, stole the land from the indigenous peoples, then divided it up and gave or sold it to European colonists, and it has been on-sold and repeatedly subdivided since – so if land titles founded on theft are invalid, land titles where you are must be just as invalid as those over here.
In Argentina and Chile, mapuche people to this day continue to legally challenge the ownership of land that they claim is theirs even after hundreds of years of having lost it to the genocide of their people -and dozens of others- as part of the creation of our nations.
In Uruguay, where I now live, this is very rarely still the case, mostly because the people who would have a right to challenge those lands ownership were very thoroughly murdered and their descendents have long been stripped of that right.
We're just not ok with brutalizing people as a business strategy. Like I said, it's a cultural thing.