“the secessionists didn’t come into play until Lincoln was elected”
That is simply not true. The secession was planned in the 1850’s long before Lincoln. Read The Road to Disunion: Volume II: Secessionists Triumphant, 1854-1861.
https://www.amazon.com/Road-Disunion-Secessionists-Triumphant-1854-1861/dp/019537018X
Read about the Knights of the Golden Circle. Read about Jefferson Davis, Caleb Cushing and the many others involved in the secession.
I don't think Freehling viewed secession as inevitable as you do. Sure it was talked about by various states in moments of frustration, but even during the Hartford Convention in 1814 or the Nullification Crisis in 1832 secession was not the primary goal. It wasn't until the Republican win in 1860 did the South put actions behind their words. Had Douglas or Breckenridge won then secession wouldn't have been mentioned much less acted upon.