A reader writes:

The implication of Millman's quoted comments is abhorrent - that the "purely practical" violence and brutality of slavery is secondary to the "hugely negative" ideological impact of the 3/5 compromise.  I wonder if he imagines slaves sitting in their lounge chairs reading the Constitution by firelight, their excited and expectant faces dropping with their self-esteem once they realize the document codifies them as but 60% of a person.  They'd probably be too depressed to work in the fields the next day!

Another elaborates:

Your reader is right, and Noah Millman is wrong.