It's pretty simple. There were Democrats that did not succeed from the Union. There were Democrats in the North. Both state and federal, the latter being rare but easy to overlook. The South voted pretty consistently and independently for a time until about the middle of the last century. Democrats gained much of the the coastal states while Republicans dominate the middle. Blaming the Democrats for the Civil War is ludicrous. If anything, one should blame the slave owners and the pro-slavery officials who were, yes, Democrats. But that doesn't mean all Democrats. There is nothing inherently wrong with voting Democrat. One should consider a politicians individual platforms rather than assume they'll just be a token party member. At least, that was how it use to before the last decade or so.
Even if you were to argue that the Civil War was not about slavery, another ludicrous notion, but ridiculously common... especially among Southern Republicans, then your rhetoric would be against the North and the political party that, at the time was attacking the "State's Rights" of the Southern Democrats which was predominantly REPUBLICAN! But that would be just as dumb as blaming Democrats for the Civil War, which again, no one should really blame the parties for that but rather the individual politicians of the time who were just trying to appeal to a group of people who don't technically exist in the United States anymore. Slave owners.
I hope that clears up for you why Democrats are not necessarily traitors.
But do you know who are traitors? People who waved the Confederate flag.
Why would anyone celebrate a flag of traitors. Even if you wave it WITH the American flag, the message is dubious at best.
