This infernal traffic originated in the avarice of British Merchants. The British Govt. constantly checked the attempts of Virginia to put a stop to it. The present question concerns not the importing States alone but the whole Union. The evil of having slaves was experienced during the late war. had slaves been treated as they might have been by the Enemy, they would have proved dangerous instruments in their hands. But their folly dealt by the slaves, as it did by the Tories. He mentioned the dangerous insurrections of the slaves in Greece and Sicily; and the instructions given by Cromwell to the Commissioners sent to Virginia, to arm the servants & slaves, in case other means of obtaining its submission should fail. Maryland & Virginia he said had already prohibited the importation of slaves expressly. North Carolina had done the same in substance. All this would be in vain if South Carolina & Georgia be at liberty to import. The Western people are already calling out for slaves for their new lands, and will fill that Country with slaves if they can be got through South Carolina & Georgia. Slavery discourages arts & manufactures. The poor despise labor when performed by slaves. They prevent the immigration of Whites, who really enrich & strengthen a Country. They produce the most pernicious effect on manners. Every master of slaves is born a petty tyrant. They bring the judgement of heaven upon a country. As nations can not be rewarded or punished in the next world they must be in this. By an inevitable chain of causes & effects providence punishes national sins, by national calamities. He lamented that some of our Eastern brethren had from a lust of gain embarked in this nefarious traffic. As to the States being in possession of the Right to import, this was the case with many other rights, now to be properly given up. He held it essential in every point of view that the Genl. Govt. should have power to prevent the increase of slavery.
George Mason of Virginia
August 22 1787
Debates in the Federal Convention of 1787 as reported by James Madison
Documents Illustrative of the Formation of the Union of the American States, pages 589-590
Government Printing Office, Washington, 1927