This is true of many liberals, but not him. He probably understands full well that it was put in place to protect citizens from a tyrannical government, which is why he hates it.
On the other hand, I believe he is one of those jackasses that trots out the 3/5 Compromise of 1787 as evidence of institutional racism against blacks, when the compromise is really evidence of just the opposite, that there were people in the federal government who were trying to eradicate slavery.
Since slaves had no rights, they should not have been counted as all (any more than "Indians not taxed" were) but the compromise was made to win the support of the states with large slave populations for the Constitution.