WHoa....
The Founders did not impose slavery.
The imposition of slavery was done far away; the sale of the slaves conducted on these shores. The bottom line is that the Founders did not impose an institution which continued to exist after the Revolution, and though stopping it was discussed, that did not happen.
Still, the only difference such an early manumission would have produced in today's climate is that the institution being blamed for modern cultural failures would be another 80 years removed from the present.
If something which ceased 150 years ago can be blamed, what's a few more decades?
The 3/5th person is about as imposed as it gets.