About half didn't. The other half, the ones associated with the cause the players were protesting, were fighting to keep slavery in place.
Well that is just factually incorrect. The Northern side began the war with their leader proclaiming that he had no authority to change the Constitutionally protected practice of slavery. Presumably if he was "preserving the Union", he was requiring obedience to Constitutional law, which is the very essence of the Union.
He was therefore requiring obedience to the pro-slavery clause in the Constitution as much as the rest of the document.
Indeed, his own Emancipation Proclamation excepted every area under Union control, just as constitutional law would have required for every Constitutional jurisdiction.
“About half didn’t. The other half, the ones associated with the cause the players were protesting, were fighting to keep slavery in place.”
If the South was fighting for slavery, who was fighting against slavery?