Well in that case the colonists were the bad guys in the fight against Britain. After all, one of their complains against England in the Declaration of Independence was that Britain was encouraging slave insurrections. And when the British troops marched on the colonies they offered freedom to any slaves who joined their side and fought with them. All that rot about liberty and independence that the colonists were talking about was really just about slavery.
In a limited sense I suppose one could consider the colonial Revolutionaries to be “the bad guys” because they were rebelling against authority, but their cause - the struggle against tyranny - was just and righteous even if imperfect. The same cannot be said of the southern insurrectionists.