Scenario B's transaction was synthetic in the form of a 'gift' and assumed to be over a very short period of time where all three people are alive. Person C in Scenario B has the ability to give back to Person B.

Scenario A's transaction took place far too long ago where the parties of the original contract are dead. The descendants of the original contract are far past the statute of limitations, the descendants of which can be both from slave-owners and slaves. There would be far too many descendants born into a frivolous contract ex machina. Are you prepared to waste money performing DNA testing on all the descendants in the United States and crosscheck slave-owner/slave identity?

The real scary thing is the 41% who voted yes to the first poll. Sins of the Fathers much?