part of a letter from Ben Franklin to John Collins, Gov. of Rhode Island. The letter is dated 12 Jan 1788
“The Society have heard with great distress that a considerable part of the Slaves who have been sold in the Southern States since the establishment of the Peace have been imported in vessels fitted out in the State over which your Excellency presides”
And what do Franklin’s writings in 1788 have to do with the southern states leaving the Union in 1861 so that they could maintain slavery?
Would those ships have been fitted out to begin with if they hadn't been able to sell all those slaves to the Southern States? That's basic capitalism - where there is demand then someone will supply it. No demand, no supply.