Yep, farming was already becoming mechanized with the cotton gin and the reaper. Slavery is evil, but technology would have probably made plantation slaves uneconomical within a decade, and the opposition to abolition (which was largely economical, coming from southern agriculture) would have vanished. England abolished slavery without a bloody war.

Also, secession was not treason. Secession was part of American culture, and the concept was laid out clearly in our own Declaration of Independence. There were many secession movements prior to the Civil War, some were abolitionist, but none ever got enough votes for states to leave the union. The writings from the time clearly show that secession was considered legal, and a viable option, as government by and for the people was our core value, one that we have lost.

I'm convinced the Civil War was more about keeping and consolidating the Federal government's power over the states.