I have told all my kids that I am proud of them that they find topics that go against the normal cultural grain, and that they hold their ground. I see the biggest divide with them and their peers in the liberal/conservative issues (we live in a very liberal area), and also the moral aspects of things.
But pretty cool when a friend asks “How come you don't swear?”
Congratulations.
Your son is right. It is pretty well known that slaves were not sent into the holds of tobacco ships being loaded: the hogsheads being loaded (Barrels 14 ft. long and ten ft. or more in diameter—the shipping containers of the day) could shift and crush someone, and the slaves represented an investment. It is no accident that dangerous jobs such as teamster, longshoreman, cop, and powder monkey (to name a few) ended up being taken by Irish and other immigrants—they were cheaper to replace.