As of 1807 slave ships were outlawed, and considers pirates. Thus the ships were not U.S., nor UK flagged ships.
but there were slave ships carrying the stars and stripes before 1807. Just as it flew out west against the Indians.
if one wants to be offended then one should look at the stars and bars as that was the official flag of the confederacy. The battle flag was just that , a battle flag.
Erie was an American owned and crewed ship. Her Captain, the owner, was born in the State of Maine. Of course it was illegal for Americans to engage in the slave trade. But it was done. The slaves on the Erie were bound for Cuba.