There's a good piece at Huffington Post about McCain's slave owning ancestors: http://www.huffingtonpost.com/abby-ferber/does-it-matter-that-mccai_b_136872.html
I was a little disappointed because I was half expecting to find out that McCain himself kept some slaves in his many mansions.
The point is that the McCains continued to be well to do after the slaves were freed, while their former slaves struggled. The legacy of slavery is still with us. It's not that white folks with slave owning ancestors should feel guilty about it; it's that we should acknowledge that the freed slaves were not in very good shape economically when they were emancipated and that a century of Jim Crow made it very hard for them to get ahead. They never did get that 40 acres and a mule that was discussed. Even with civil rights legislation, there is still a great deal of discrimination against the descendants of the slaves, so there's little wonder that black folks are on average poorer than white folks.
Most of my ancestors were illiterate dirt farmers and didn't own any slaves. They were mostly hillbillies and lived in areas where slavery was less common than on the piedmont or tidewater. Slavery was bad for them because they had to compete with slave labor. Some of my ancestors, however, were slave owners, and I have checked to see whether I personally benefit from their crimes. My family's circumstances were such that the wealth generated by slavery went to other branches of the family and did not trickle down to me or even to any of my great great grandparents. They all pretty much had to start over after the War Between the States, and the advantages I enjoyed were due to my grandparents' hard work that saw them rise from sharecropping to owning their own farm. Of course, if they had been black, I'd have been a sharecropper, too. Black folks in my home town didn't have a chance of getting ahead. White folks literally would not let them.