I do not believe that the Constitution was stained.
The Founding Fathers placed humans in three catagories; Voting Citizens, Non-Voting Citizens, and Non-Citizens. Non-Voting Citizens could aspire to become Voting Citizens through hard work. Life was not as good for Non-Citizens, but their existence in the US was probably, on average, much more pleasant than as slaves back in their home countries. Slaves were not created in America; they were imported. Even slaves had the potential to buy their freedom. This system was more fair than anything that preceded it.
Because of the surpluses that the Founders’ system created, we have been able to make ourselves feel better by making the system more equitable. Unfortunately, in a universal democracy, the electorate always learns to vote itself benefits that the treasury cannot afford. Thus pure democracies are inherently unstable and fall apart in internal civil conflict.
We’ll be lucky if we still have the freedoms presented to us in 1789 when the smoke clears. Slavery is a natural human condition.