I'm away from home, in South Dakota this week. The McCullough book is at home. Next week will look it up and see if I remembered correctly. If so, will provide you with quotes. If not, will apologize for confusing the issue. ;-)
My point here is, the need to abolish slavery was recognized by our Founding Fathers, even those from the South, such as Jefferson, Madison and Washington. This necessity was passed down from father to son -- literally in the case of John Adams to his son John Quincy Adams -- and eventually to the new generation represented by young Whig Congressman Abraham Lincoln.
The the issue was never "whether" to abolish slavery, but rather "how" and "when." And, as I spelled out, there were at least three theoretically possible ways, but tragically, only one of them practical enough to actually happen -- a War of Southern Rebellion.
The need that was recognized was the cooperation of the States in forming a new Union.
The terms of Union were the terms of Union.
And the idea of coercing a State was abhorrent to all of them. Recognize that.
The Framers -- the Framers of the Constitution, you do know who I'm talking about? The participants in the Philadelphia Convention, and the ratification conventions? And Jefferson pro honore, even though he was serving as United States ambassador in Paris? -- all recognized that a Union founded on coercion was in fact an empire, and that coercion -- read your political theory sometime -- nullified the social contract. That was Locke, and everyone after him. Until Lincoln. And, as you say, John Quincy Adams, and the sophistry of "well, that was then, but this is now."