I've never fully understood the southern USA obsession with treason, until the NY Times ran a series where the published article on the day 150 years ago leading up to, and during the US Civil war.
First, although it was later whitewashed to say the war was over states rights, it turns put the only state right mention in any article of secession was the right to slavery.
Second, it also explained why the dirt poor southerners who were not slave holders fought so hard - it was about their social status, knowing they were "superior" to someone (i.e., black slaves).
Third, it also explained that the US south was showing great strides toward economic/political power for freed black americans (there were elected US congressman who were black, etc) until around 1876, when reconstruction ended and then using terror (The klan) and other voter suppression (grandfather clauses, poll taxes) methods extinguished black political power. Then Jim crow laws/segregation to codify it.
Fourth, the myth of the lost cause (trying to make treason seem "noble") was spread around the turn of the century and for the most part bought into by the full country as a means to reincorporate the south more fully back into the country. Here is where they start to see the statues and place naming for confederate generals and confederate flags, etc.this accelerated after WWI when black soldiers returned from Europe hoping for expanded rights after fighting in the war.
Fifth, as the civil rights movement starts in earnest after WWII, then more statues and more displays of the confederate battle flag emerge throughout the south as a symbol of resistance to civil rights. Thus they start showing up on state capitol buildings and everywhere else.
Thus it seems to be a relatively more recent phenomenon (last 75 years), and the whitewashing of the history of it for white people has many white Americans seeing it as an innocuous display of personal independence. However, to black Americans it's original meaning has never been lost - white people willing to die in order to keep black people enslaved. And it seems now many more white americans are seeing that flag for what it is.
General/President US Grant said it best: "I felt like anything rather than rejoicing at the downfall of a foe who had fought so long and valiantly, and had suffered so much for a cause, though that cause was, I believe, one of the worst for which a people ever fought, and one for which there was the least excuse."
Anyhow, living outside and inside the USA gave me a wider take on this than my American friends. But it always struck me as a flag of treason.