By 1860, public opinion had shifted enough from 1783 that northerners were no longer willing to compromise on fugitive slaves, or on the expansion of slavery into new territories. There wasn’t yet a majority for abolition, but the lines had definitely shifted to the point where there was no longer an acceptable middle ground.
Two points.
First point. There was no compromise on the issue of fugitive slaves. The US Constitution REQUIRED they be returned to their masters. The only choice states had was whether they were going to obey constitutional law, or refuse to obey constitutional law. (Which is rebellion.)
Second Point. Slavery was not going to "expand." There was no place where plantation slavery could go to add new cotton crops beyond where it already existed.
This is not absolutely true. A teeny portion of southern Kansas can grow cotton in modern times, but it doesn't amount to much in the larger cotton crops, and there is no guarantee it could have grown cotton then.
Cotton cannot be grown in any other territory in 1860. It was actually impossible. No cotton, no "expansion" of slavery into the territories.
The whole thing it appears, was a lie created for the purpose of keeping the Southern representation a minority in Congress. The entity most responsible for spreading this claim of "slavery expansion" was the "Free Soil Party."
Which was headquartered in New York New York.
It wasn't in Kansas. it wasn't even in Chicago. It was in the city which stood the most to gain by keeping the Southern representation in Congress as small as possible.
It was a thousand miles away from the territory in question.
There wasn’t yet a majority for abolition,
And there never was going to be in this era. They wouldn't have been able to even pass the 13th amendment without putting guns in the backs of legislators and forcing them to vote for this thing which all the Northern side has been claiming ever since the South was fighting to prevent.
We are led to believe that the Southern states fought only to keep slavery, and yet they would simply give it up willingly by a vote?
No. Without duress, it was impossible to reach the required 3/4ths majority to pass the 13th amendment.
All the Southern states which voted for it were simply puppets of the DC government, and they were voting as they were ordered to do instead of espousing the actual will of the people.
That is *NOT* how the founders meant for amendments to be passed. When they are coerced, they are illegitimate.
In 1860 the "middle ground" for Republicans was: there will be no expansion of slavery, period, not into western territories nor into Northern states via SCOTUS Dred Scott type rulings. Fugitive slaves were the responsibility of Federal government, which could compel (and pay) local authorities to comply with Federal laws.
Southern slavocrats saw this "middle ground" as an existential threat to their "way of life" and reacted accordingly.