NEVER forget this!!!! The 3/5 clause is an ANTI-SLAVERY, ANTI-SLAVEHOLDER provision. The number of people who do NOT know this is staggeringly huge.
Its primary concern was over taxation and representation not slavery.
Indeed. It was to limit the number of representatives the slaveholding states would have in Congress. It was a compromise between the non slave states who wanted the slaves to not be counted at all and the slave states that wanted all the slaves counted so that they would bring more proslavery representatives to Congress and thus make things like limiting the exportation of slavery to the territories impossible or at least much harder to accomplish. The compromise kept the slave states from being overwhelmed ab initio in Congress while not permitting them to overwhelm the antislavery states. Anything else would have precluded the Union.