"...And yet he led his men to slaughter fighting for a state's right to determine something that he did not agree with."Exactly!
The alternative to this would imply that a state has only those rights that you would agree with? how principled would that be?
This seems to be pretty close to the idea that I would defend to the death YOUR right to espouse wrong ideas. I may not agree with you, but I'll defend your right to be wrong.
As much as I appreciate your defense of my right to speak freely, it is simply inhuman to compare this philosophical arguement to the defense a state's right to allow something as morally reprehensible as slavery.