You wrote "Outright abolition was still a fringe policy at the beginning of the war."
Why do you believe that? All of the declarations of succession I've argue otherwise.
Georgia's says "The feeling of anti-slavery, which it was well known was very general among the people of the North, had been long dormant or passive; it needed only a question to arouse it into aggressive activity."
Mississippi's says "until the whole popular mind of the North is excited and inflamed with prejudice" against "the institution of slavery-- the greatest material interest of the world".
You wrote "none of these seem to imply that their authors believed that abolition was imminent (in the next 4 years or so)."
The documents of succession are clear that they don't want to be under Lincoln, with the Republican party in control.
Mississippi's says "There was no choice left us but submission to the mandates of abolition, or a dissolution of the Union"." They are clear that if they stay in the Union then they are certain abolition will come.
South Carolina specifically named "On the 4th day of March next" as the day when "The guaranties of the Constitution will then no longer exist; the equal rights of the States will be lost. The slaveholding States will no longer have the power of self-government, or self-protection, and the Federal Government will have become their enemy."
Georgia again: "Such are the opinions and such are the practices of the Republican party, who have been called by their own votes to administer the Federal Government under the Constitution of the United States. We know their treachery; we know the shallow pretenses under which they daily disregard its plainest obligations. If we submit to them it will be our fault and not theirs. ... because their avowed purpose is to subvert our society and subject us not only to the loss of our property but the destruction of ourselves, our wives, and our children, and the desolation of our homes, our altars, and our firesides. To avoid these evils we resume the powers which our fathers delegated to the Government of the United States, and henceforth will seek new safeguards for our liberty, equality, security, and tranquillity."
These aren't people thinking they can wait until the next election to see what happens, and perhaps they can decide to succeed then. These are people convinced that if they stay with the Union any longer then their entire way of life will be destroyed. That's why seven states succeed before Lincoln was inaugurated.
How do you get from those statements to "none of these seem to imply that their authors believed that abolition was imminent (in the next 4 years or so)"?
You commented;
> Does not change the fact that immediate abolition was politically infeasible (which is something Lincoln himself reiterated during his inaugural address and I have to reiterate that while opposed to slavery Lincoln himself was not an abolitionist and did not run on abolitionist ticket).
That's not relevant because my comments all concern chargingmarmot's claim at https://news.ycombinator.com/item?id=37383422 , concerning the reasons for why the South succeeded.
That those reasons may be ill-founded is a different discussion, while I want to stay on topic as Civil War discussions have consumed countless hours.
The fact is, many of the states which succeeded did do because they want to keep slavery, as they very clearly justified at the time. The injustices they felt were because they (correctly!) thought that the Constitution was created to preserve slavery, and that compact was no longer being followed.
If you conjecture it was merely "politically advantageous" and they didn't actually believe it, then you aren't taking this seriously and presenting solid evidence to support your conjecture.
Otherwise, are we also to take racist nonsense like
> We hold as undeniable truths that the governments of the various States, and of the confederacy itself, were established exclusively by the white race, for themselves and their posterity; that the African race had no agency in their establishment; that they were rightfully held and regarded as an inferior and dependent race, and in that condition only could their existence in this country be rendered beneficial or tolerable.
as more political posturing that they didn't actually believe?