You are turning history upside down. Under the Constitution the more heads a state could count, the more representatives in congress it would have. Those opposed to slavery argued that slaves should not count since they were represented. The large slave holding states argued that everyone should count. The compromise reached in the Constitutional Convention was to count slaves as 3/5 of a person.
BUT........... that 3/5 number had a history.
Only four years earlier in 1783 an amendment to the Articles of Confederation was proposed to change the basis for determining the wealth of each state, and hence its tax obligations, from real estate to total population. At that time, the large slave states argued that slaves should not count. The other states argued that everyone should count.
A compromise was reached that called for counting slaves as 3/5 of a person. The amendment eventually failed falling two states short of the unanimous approval required for amending the Articles of Confederation (New Hampshire and New York were opposed). But all of the large slave states supported it.
So when it came to paying taxes on their 'chattel property' they did not want them counted. But when that same chattel could mean more power in Congress, they wanted slaves counted. And in both instances, they were willing to go with the 3/5 count.
Great post.
However, the quote the attributed to me was not mine.