I doubt we disagree.
Certainly Southerners saw Republicans as a threat to slavery in the South.
But I would challenge you to look at the Republican party 1860 platform itself and find anything there which threatened slavery in slave states.
No, the issue for Republicans in 1860 was not rolling back slavery, but rather preventing the expansion of slavery into non-slave territories, plus the enforcement of fugitive slave laws in non-slave states, as directed by the Supreme Court's Dred-Scott decision.
Yes, of course, the old Southern Democrat Slave Power (S.P.) claimed that any legal restrictions on expansion were an attack on SLAVERY, just as today the new Democrat Secular Progressives (S.P.) claim that any restrictions on the Power of Government is a "war on women", or racism, or "throw grandma off the bridge," etc.
In short, the Constitution had survived for 70+ years recognizing the rights of some states to legalize slavery and others to outlaw it.
What changed by 1860 was not Northerners' intentions to attack Southern slavery, but rather the Slave Power's insistence that slavery should not be restricted anywhere.
Now, do you still say we disagree?
Pretty much I guess we agree. But again, you have to see Huston’s book to see, regardless of what the Republicans said, how inevitable the fight over the definition of property rights was and how, eventually, this would force the Republicans to act. Hey, I’m not trying to argue that the North was at fault, but I do not think the South’s interpretation of the near future was wrong. When you say “we lasted 70 years,” well, that included a ban on doing anything about the slave trade for 20 of those years, then of the remaining 50, the Van Buren party system accounted for 42 of them. The surprise is not that it fell apart, but that Van Buren’s shenanigans actually kept it together so long.
Well, isn't this the same thing we see with anti-gay "hate speech?" Merely quoting the Bible is now considered a "hate crime" in Canada and Scandinavia when it comes to homosexuality.