Hmm... I don't think humanity's terminal values have changed very much since Benjamin Franklin (matter of fact, he was an Enlightenment figure, and the enlightenment is probably the most recent shift of terminal values in the Western world: political liberty, scientific truth, etc.) The things that I imagine would horrify him are mostly either actually bad (Global warming! Nuclear bombs!) or a result of cultural taboos or moral injucntions that have been lifted since his time (Gay marriage! Barack Obama!). This, it seems, is what we mostly mean by moral progress: The lifting of {cultural taboos/moral injunctions} which inhibit our terminal moral values.