"There is nothing which I dread so much as a division of the republic into two great parties, each arranged under its leader, and concerting measures in opposition to each other. This, in my humble apprehension, it to be dreaded as the greatest political evil under our Constitution." óJohn Adams
While you are obviously keen to make this a North/South issue, and thats fine, it is really a Republican versus Democrat issue and, even according to your own post, it was the Democrats who were the racists, disavowing Lincoln's struggles until just recently. A million excuses won't change the facts.
John F. Kennedy (with Johnson actually signing the legislation) is a huge hero in African-American households. As was his brother Bobby Kennedy. Bobby Kennedy was in my hometown of Indianapolis on the night of Dr. King's assassination. He delivered the news to a large crowd (mostly inner-city blacks) that Dr. King had been killed. Indianapolis was the only city of major size to have no riots on that night. Robert Kennedy: Delivering News of King's Death : NPR
They were Democrats. That's not that hard to figure out. It doesn't help that Strom Thurmond (who ran for president specifically on a segregationist platform in 1948) switched to the Republican Party in 1964 as a result of the passage of Civil Rights legislation. And with him, South Carolina flipped from Democrat to Republican.
So, were Democrats the more racist party in the South at one point? Yes. Upon passage of the Civil Rights legislation of the early 1960s, they flipped to the Republican Party. For instance, Kennedy (a integrationalist Democrat) barely one South Carolina, and Republicans have won every election ever since.
Our Constitution was made only for a moral and religious people. It is wholly inadequate to the government of any other.
Yes, the South did change from solid Democrat to Republican but that could also be construed as them being eager to get rid of their racist past and start afresh with new beginnings. I believe that's been the attitude of the South since then, though remnants remain.