The American colonists wanted more rights granted to them as subjects of the crown and an end to onerous taxes. That was not forth coming from the Crown. The South wanted to preserve an economic system based on the use of slave labor. They certainly weren’t advocating rights for slaves. They choose armed rebellion against a duly elected government. Rebellion to achieve independence and human rights from a degenerate monarchy doesn’t count as treason to me.
"Rights" do not have qualifications. If you have a right to do something, you don't have to have a "good reason" to exercise that right. It is your right to do it regardless.
The founders declared that independence was such a right. Therefore a people's reasons for wanting it are irrelevant. They have an inherent right to independence and they do not have to justify it.