> That’s close enough to the notion that supporters of slavery deserve credit for the abolition of slavery, because without slavery existing it never could have been abolished
Um, that's not remotely close to what's being contended here. What we're talking about is tradeoffs; i.e. what do you do when you want to coerce other States to abolish a regime that's politically unpopular in your State, but politically popular in the State in question? You can either do nothing, and let that system continue to exist (in perpetuity), or you can set up a new system that enables us to eventually abolish that institution from the top-down.
You have to consider the alternative: Founders that didn't create a Union, an independent South, and no real incentive or force to act as a check on slavery, and potentially allowing it to exist in the South beyond the 1860's. This is a hypothetical that's pretty easy to imagine considering that those Southern states tried creating a Confederation with slavery literally being enshrined in its Constitution (a "founding pillar", to use your framing) in 1861.
A world in which the South just agrees to join the Union in 1787 and also simply agree to abolish slavery is a fantasy. A world in which the North creates a slavery-free Union without the South is one in which slavery exists in a Confederate constitution well past the 1860's. Given those options, I'll take our reality any day of the year: the one where we created a Union that allowed us to eventually outnumber the South, elect Abraham Lincoln, and abolish slavery once and for all. That was the Founders' gambit, and the Confederates admitted just as much in their Cornerstone Speech I cited above.