I always appreciate irreverent observances of Confederate "heritage" days:
In the real world, white Unionists in the free states largely shared basic white supremacist ideas with Southern slaveholders and their supporters. Although the dominant propaganda justification for slavery in the South in 1860 was a more intense and toxic version that held black people to be permanently suited only for slavery. And the rejection of democratic principles that implied was leading the slave states farther and farther away from democracy for whites, as well.
But slavery was a distinct issue. And by the end of the Civil War, many Union soldiers had not only seen the horrors of the Civil War that the slaveowners brought on to defend their Peculiar Institution, as they called it. Many of them had their first contact or extensive involvement with slaves, and had seen black Union troops performing bravely and ably in the Union cause, while the defenders of slavery were killing US soldiers in the service of treason.
So many Northerners who had previously been indifferent to slavery or not especially concerned about seeing it ended before the war now deeply despised it and understood its destructive effects on a democratic Republic like the United States.