@MontereyJack,
If the Framers had allowed each slave to count as a whole person, slavery would still exist today, as the south would have most of the country's electoral districts apportioned to them and thereby would always be able to block any attempt to repeal slavery.
With slavery secure and unending, the south would never had felt a need to secede. There never would have been a civil war, and slavery would still be a part of modern life.
If the Framers had insisted that a slave not count as a person at all, the south would have never ratified the Constitution. The north and south would have formed separate countries from the start, and the southern country would still have slavery today.