Why were the “wrong” states on either side of the three fifths compromise?!

What surprises students about the three-fifths compromise is that it was the southern states that advocated counting all the slaves, and the northern states that insisted on counting not one slave. The reason it surprises many is that most Americans see the three-fifths compromise as a philosophical statement on the value of black and white people; a declaration that a black person has three-fifths the value of a white person. Within this (incorrect) conception, students expect the slave states to set the value of slave lives at zero, and the free states in the North to push for counting all slaves, seeing them as equal in their humanity to white citizens.