Source docs point out many Democrats were pro-union (esp. up North), and the election of Lincoln resulting in secession was not a foregone conclusion, though many state leaders were pulsing the issue.
It's really tough to paint the 1860 Democrats with a broad brush considering they ran 3 candidates with mixed views. The donkeys back then were very different than those of today.
What you are ignoring when you say that secession following Lincoln's election was not a foregone conclusion is History. quod erat demonstrandum
He was elected and the southern democrats unhappy with the results seceded like a bunch of children taking their ball of cotton and running home.
The reason I can paint the Democrats of that era with such a broad brush is a single common denominator, they all were in favor the continuation of slavery by any means where as The republican party was created to end slavery. The Northern democrats just weren't willing to break up the union into a bunch of little nations to do so.
Ultimately when you trim away the fat from the issue of secession, what remains is that Southern Democrats seceded from the United States in order to protect their "right" to keep men, women, and children enslaved as private property before laws ending that "right" could be written.
When defend their right to secede you are defending their right to keep a whole race of people enslaved for the sake of their business profits.
Honestly are you willing to do that, are you willing to defend slavery as a legitimate business practice and can you justify those laws Republicans risked the very union of this country to abolish?
I ask you now because sooner or later we are going to face the same sort of battle when Republicans seek to end the right to murder children in the womb. Another so called "right" the democrats have forced upon this country. Will you decide then that Democrats have the right to secede in order to protect their "right" to kill the unborn?
A very factual and reasoned argument. One thing missing though is the fact that Lincoln offered to let slavery stand and not interfere if the South would agree not to secede. The South refused. A counter offer was made that the South would abolish slavery if southern states would be left in peace to secede. The Union refused. This seems to suggest that slavery was not initially the major issue or cause for the war to either the South or the North.