I think it's pretty rock-solid that the Southern states were absolutely fighting for a nation that would allow slavery to go on as long as it wanted. I don't think even Kiting is denying that.
However, they lost the war. And, very few people in the North truly understand the ramifications of all the loss. They can't. They can't because their homes were not left in ashes. Average people bear the brunt of loss in all wars. And, as in all wars, the people who fought and died (the vast majority), were average people who had no access to the financial benefits of the outcome. They never do, never have, and never will. But, they are the ones who do all the actual fighting and dying and sacrificing in any war. They make up the majority... the vast majority.
So, after they experience defeat, are left with their homes (not just plantations, but entire cities) in ruin and ashes, an economy and society that is bankrupt and poverty-stricken, a lifestyle and culture that has disappeared, they are also left with a rancor. They are forced back in to a country that they see as their conquerors- and as invaders. The blacks become scapegoats for the misery as well. But, whatever pride or heritage or elements of their society they are able to reflect upon with happiness becomes something for them to symbolize. Their flag becomes a consideration. There is still, to this day, a resistance and token contempt toward the "USA" by many Southerners. That is indicative of how much destruction was done and how demoralized the populace had become. So, even though the KKK uses it for their hate, the rest of southern society, that is not as hate-driven about placing blame on blacks, still have a fondness for the flag because they lost a lot because of the war as well... and it wasn't the ability to own slaves, because, like in modern days, very few Southerners owned anything.
The South practically lost EVERYTHING IT HAD. Now, you can say "they had it coming", and I would agree that their desire to maintain an institution of slavery was wrong. I still maintain that war was and is the wrong way to fix things in a civilized society. BUT... the other aspects of their life were not rooted in oppressing other human beings. There is a great many cultural things that are "Southern" that aren't based in slavery.
Believe it or not, the entire nation, save for abolitionists (who, in my opinion are truly the heroes), were of the belief that Africans were inferior humans by nature! North, South, East and West had that opinion. In fact, the same whites that were allegedly freeing blacks went to work killing another color/race of humans in the west as soon as operations were over finished here. Regardless, not all Southerners associate keeping Africans as a subjugated class when they see or display that flag. Just because YOU see it that way, doesn't mean EVERYONE sees it that way. If you want to ostracize them, fine. But, at least try to observe that they are not advocating slavery, even though you don't like their symbol.