Vasco runs a slave ship along the Slaver's Coast, port to port, filling his hold a few captives at a time until it is worth the crossing north. He is a competent sailor and a wholly unremarkable man, and that is the point of him. To Vasco the trade is not cruelty or commerce or sin. It is the route he learned, the cargo that pays, and the weather he has to beat. He no more agonizes over what is chained below his deck than a carter agonizes over the weight of his load.
His circuit is the standard one. He works the small extraction ports of the southern coast, takes on Drasnian dwarves from the holding pens, and runs for Divinity Passage by way of the Torgan Passage when the eastern ports are full. To keep the run smooth he pays into the Slavewatch garrison's comfort fund, and in return Tribune Volso's people tell him which ports are accepting cargo, which are temporarily closed, and when the imperial inspectors will be looking. It is an ordinary business expense. Vasco budgets for it the way he budgets for rope.
There is exactly one thing that can make Vasco's voice change, and it is the dragon Agtakkeri. The dark green dragon has sunk two of his ships out from under him, both at dawn, both with the cargo still chained when the water came in. Vasco swam clear twice and watched both holds go down full. He does not call the dragon by name if he can help it. He spits over the rail at first light, every morning he is at sea, and he will not run the northern approaches for any fee Volso could name.
Twice she took my deck out from under my boots. Twice I came up spitting brine with men screaming behind me in the dark, and they were not screaming at me, they were screaming at her. Pay the Tribune all you like. There is no fee that buys you past the Skinning Wind. — Vasco, in a Slaver's Coast dockside tavern
He has never once thought about who drowned in those holds. The two ships were a loss of property and a loss of standing, and the dwarves chained in them do not enter his accounting at all. This is the whole horror of Vasco. He is not a sadist or a zealot. He is a working captain who would be unremarkable in any honest trade, and the trade he happens to work is the worst one on the island. The freed who slip through Agtakkeri's waters bless the dragon for the same dawns that cost Vasco his ships, and he would not understand why anyone would.