It wouldn't surprise me if he was into abusing slaves because it was a good ol' boys' club. Franklin did inherent several slaves, got to know them, realized they were people, freed them, then became an abolishinist.

At the end of the day, however, he still agreed with the 3/5ths. Compromise. And he was still buddies with monsters like Washington and Jefferson. Otherwise, everything we know about his sexual history points to him wanting older women, which is part of why he wanted the ambassadorship to France.