Louis XXIV
Le Roi Soleil
If we had talked about 'black slaves' rather than 'slavery' that counter-stoke might have some merit. Since we didn't, it doesn't.
The other point that needs to be stressed is the whole institution was predicated on the idea that it was fine to own slaves, so long as those slaves were black. Consider what Chief Justice Taney said in Dred Scott: [blacks were] beings of an inferior order, and altogether unfit to associate with the white race, either in social or political relations, and so far inferior that they had no rights which the white man was bound to respect. The racism literally drips out of that statement and the system continued to survive because most Southerners, and some Northerners, believed that was indeed the case.
Chief Justice Taney was influenced by Calhoun, who was a big proponent of scientific racism. His work does an amazing job of not only attacking abolitionists, but discrediting even people like Thomas Jefferson (all men are not born free and equal, they are born infants and have to grow to become men. Since blacks are of a "lesser race" they can never reach this point). There's quite honestly a clear line between Calhoun and Hitler. Taney was never quite as bad because he didn't have the intellectual capacity to go that far. But he did buy the notion that Southern slavery was justified because it was African slavery (contradicting the English tradition of slavery only existing because of positive law and had nothing to do with race).
As far as northerners fighting to end slavery. There's no question that Lincoln was careful at first to say it wasn't about slavery. However, there's no way to ignore the impact the Emancipation Proclamation had on making the war about the moral issue of slavery. This was seen in Europe, it was seen in the draft riots in New York (where people openly said they didn't want to fight a war for blacks). Lincoln was a political pragmatist who avoided saying things that the majority of Americans disagreed with and only acted when he had political support. So while I agree that preservation of the Union was always the primary goal, I do think he began to see this as an opportunity to end slavery.