All good points, though I wouldn't call 50 years ago ancient history. For that reason I think opposition to affirmative action raises red flags in the minds of many black Christians who are otherwise social conservatives. Granted, those who most opposed integration in the South may have been Democrats, but the perception is that they were primarily conservative, fundamentalist "Christians", a group that today is associated with the religious right.
I have lived in the South all of my life and know of no church which sanctioned "lynching". Your assertion that Southern churches approved of this is an outright lie.