Even women couldn't vote, so it's not fair to say that slavery was the rationale. No reasonable person today would say that the 3/5 Compromise or denying universal suffrage is desirable.
Other commenters have also mentioned a necessity to ratify the Constitution. That also applies here as well.
> Yeah, slavery.
No, tyranny of the majority. See: https://en.wikipedia.org/wiki/Tyranny_of_the_majority
Even women couldn't vote, so it's not fair to say that slavery was the rationale. No reasonable person today would say that the 3/5 Compromise or denying universal suffrage is desirable.
Other commenters have also mentioned a necessity to ratify the Constitution. That also applies here as well.