The problem with the Slavers Secession was that it was attempted unilaterally. Knowing that the Constitution was silent on the act, but also mindful that there were others (a majority of others) who held a different attitude regarding secession, they did it anyway - using "rules" that they made up as they went along.
Even that wasn't enough to spark war, but when they illegally seized federal institutions, mints, storehouses, and forts, and then fired upon federal soldiers they forced a response from the federal government.
If you resort to force of arms and start shooting do not be surprised if someone shoots back.
“...keep in mind that your potential opponent or adversary has his natural rights as well. That’s why we have laws.”
If I were violating my adversary’s fundamental God given rights, I would expect for a system of just laws (and enforcement) to compel me to cease that activity.
Only a law which is repugnant to the natural rights of man would dictate otherwise.