This has been an interesting thread and I see validity in both sides of the issue. I'm not a Christian but I have always loved this hymn. At the graveside service for my brother I had my son take his boombox off into the woods and play a bagpipe recording of it from an unseen distance. I'm not sure if I would now, knowing what I know about the man who wrote it. Now I understand that in the 18th century being a pious Christian did not necessarily make you an abolishonist.
Many actually believed that by capturing and Christianizing the African "heathens" they were saving their souls, even as they enslaved their bodies. Some even pointed to a supposed biblical ordination of the enslavement of the black race: Gods imposition of that punishment on "the sons of Ham" after he derided his father Noah for his naked drunkenness. Hamite was a synonym for a black person well into the 19th century. That being said there does seem to be a certain amount of hypocrisy at play when a man speaks out publicly against an institution while profitting from it. He surely was aware of its brutality having been so closely involved with its practice.
    I find it hard to separate my personal feelings on a work of art from the integrity of its author. It's like when I discovered that Jack London was a racist. And I've never been able to enjoy the works of Wagner since learning of his anti-semitism, even if the conductor of the Israeli philharmonic has decided they're okay.(Beethoven is a different story. You can't fault him if some genocidal madman comes along well after his passing and enjoys his music.) Sometimes knowledge can be heartbreaking but it is still important to acquire it. Works of technology (i.e. driving your Volkswagon on the autobahn or DNA research in light of the recent racist propagandizing by James D. Watson) don't necessarily invoke the same feeling and it IS a personal feeling I'm describing. I certainly wouldn't try to stop anyone else from performing or enjoying "Amazing Grace". I'm just saying that I'll never hear it again without a certain reservation.
    On a lighter note I must disagree with artbrooks and Kim C. I've always thought "Amazing Grace" is the only song that SHOULD be allowed on the bagpipes, but don't tell my wife I said so. She loves the blasted instrument. ;^)
                           Neil