Like i said they did nothing to PREVENT or ABOLISH slavery, or the slave trade for that matter, so you are the one that is mistaken.
Thomas Jefferson, for example was a major slaveowner known for his relationship with Sally Hemmings.
The Three-Fifths compromise was a compromise between Southern and Northern states reached during the Philadelphia Convention of 1787 in which three-fifths of the population of slaves would be counted for enumeration purposes regarding both the distribution of taxes and the apportionment of the members of the United States House of Representatives. It was proposed by delegates James Wilson and Roger Sherman.
This had nothing to do with ending or abolishing slavery. It was a device used to weaken the tax base of the southern states.
The amendment was to have changed the basis for determining the wealth of each state, and hence its tax obligations, from real estate to population, as a measure of ability to produce wealth.
Now lets look at the effects:
The three-fifths ratio, or "Federal ratio" had a major effect on pre-Civil War political affairs due to the disproportionate representation of slaveholding states. For example, in 1793 slave states would have been apportioned 33 seats in the House of Representatives had the seats been assigned based on the free population; instead they were apportioned 47. In 1812, slaveholding states had 76 instead of the 59 they would have had; in 1833, 98 instead of 73. As a result, southerners dominated the Presidency, the Speakership of the House, and the Supreme Court in the period prior to the Civil War.
In effect the 3/5th actually REINFORCED slavery, particularly in the southern colonies.
http://en.wikipedia.org/wiki/Three-fifths_compromise