The irony is that always gets brought up as though it was actually meant to represent the value of the slave’s humanity.

The large slaveholding states actually wanted 5/5ths whereas states will small slave populations wanted 0/5ths. Slaves couldn’t vote, their interests were ancillary to the whole discussion. The compromise was about pure political power for those that dominated them.

The repeal of the 3/5ths clause along with the subsequent legal restrictions and terrorism against the black population of the south that followed, gave the south more power, and subsequently made it harder to dislodge Jim Crow.

But your point is still very valid. Somehow people are comfortable compartmentalizing the notion that the constitution is/was perfect, except for that one part that somehow doesn’t count and was “inevitably doomed” anyways.