If we don't go by "Founders' Original Intent", then we have nothing to anchor our understandings of what the Constitution means beyond our own definitions of their words.
And if we are free to redefine words to suit today's latest political correctness, then we end up... well just where the Obama-nation is leading.
So... Founders' Original Intent in the case of "dis-union" or "secession" is clear and consistent, as spelled out by Madison specifically and as implied in the words and actions of all others.
The Founders did not intend that "dis-union" should be "at pleasure", meaning without serious reasons, or that it should be unilateral.
What they did intend was that it should be by "mutual consent", or alternatively, as a result of "oppression" & "usurpations" -- a breach of compact -- which would "have that same effect".
In December 1860, there was neither "mutual consent" nor a breach of compact, and so Deep South Fire Eater declarations of secession were not constitutionally kosher -- they didn't pass our Founders' tests.
Nevertheless, those declarations of secession did not start a Civil War, and neither did their forming a new Confederate government.
Indeed, had the Confederacy been determined to preserve the peace, Lincoln told them in his First Inaugural (March 4, 1861) that they could only have a war if they themselves started it.
But an assault on US troops in US Fort Sumter is an act of war, and since it was soon followed by a formal declaration of war on the United States, it's abundantly clear the Confederacy did not wish to preserve the peace.
Naturally, Confederates in 1861 expected to win their war for independence, just as our Founders did in 1776.
But they were mistaken, and the rest is history...
“If we don’t go by “Founders’ Original Intent”, then we have nothing to anchor our understandings of what the Constitution means beyond our own definitions of their words.”
The founders had their disagreements amongst themselves, and it’s not hard to find passages from the founders’ writings that contradict each other. That’s why we aren’t ruled by just any old writing from the founders, but by the Constitution that they agreed upon. If you can’t find support for your claims in the Constitution, it won’t suffice to simply substitute some other writing and claim it is binding.