...the 'right' to exploit other people for their own economic gain.

Surely that wasn't a point of difference between the two sides? There were two different ideas about how exploitation ought to be done, with the chattel slavery one being even nastier than the other.

As has been pointed out, the initial war aim of Washington wasn't to abolish slavery, but to prevent secession. What is also true however is that the reason for the secession was to preserve the slave system - which was not in fact under threat.

One interesting thing is that the first serious talk of secession was in the New England states in the early years of the 19th century. At that time of course the Southern States were wholly opposed to any right of secession,such as applies in most federations.