You have, you just refuse to admit it. You *WILL NOT* admit it, but that is a decision of will, not of intellect.
It is no more valid than saying “The Smith's divorce was not about physical abuse, because Mr. Smith promised to quit beating his wife.” If Mrs. Smith does not trust her husband, and does not believe he will actually stop the violence, then she will go through with the divorce despite assurances that the violence will end.
The Fire Eaters of the South did not trust the Northern politicians, particularly Lincoln. They did not believe that the abolitionist movement would end. They feared efforts to enact state by state prohibitions outside of any federal amendment. Finally, they wanted to expand slavery and the Kansas–Nebraska Act worked against that goal.
You have proved nothing.
The other problem with making the Corwin amendment the linchpin of your position is that it totally ignores the decades long strife between free and slave states, and the fear of abolition that manifested itself in Southern politics prior to 1860.
A decade before G.E. Haynsworth fired the first shots of the Civil War, Southrons met in Nashville to consider secession. What was their reason for consideration of severing ties? It wasn’t tariffs, or New York shipping firms.
Let’s see what the members of the convention itself wrote in their official declaration.
“We, the delegates assembled from a portion of the states of this confederacy, make this exposition of the causes which have brought us together, and of the rights which the states we represent are entitled to under the compact of Union.
We have amongst us two races, marked by such distinctions of color and physical and moral qualities as for ever forbid their living together on terms of social and political equality.
The black race have been slaves from the earliest settlement of our country, and our relations of master and slave have grown up from that time. A change in those relations must end in convulsion, and the entire ruin of one or of both races.”
President Polk, himself from Tennessee, was angry that Southerners were undermining his efforts to reach a peaceful solution to the question of slavery at the time. He recalled in his diary what he had told his cabinet. “I stated that I put my face alike against southern agitators and northern fanatics and should do everything in my power to allay excitement by adjusting the question of slavery in preserving the Union.”
Alexander H. Stevens of Georgia wrote, “I find a feeling among the southern members for a dissolution of the Union-if the anti-slavery measures should be pressed to extremity…”
The Richmond Enquirer opined “The two great political parties of the country have ceased to exist in the Southern States as far as the present issue of slavery is concerned. United they will prepare, consult, combine, for prompt and decisive action.”
The Columbia Telegram wrote “…form a Southern Confederacy, in possession by force of most of all the territories suitable for slavery, which would include all south of the northern latitude of Missouri.”
https://www.americanantiquarian.org/proceedings/44806651.pdf
There are many more quotes I could provide but the intent was clear. In the minds of the Southern power structure the abolitionist movement was threatening the institution of slavery, and a growing desire to break away was afoot. The Wilmont Proviso had drawn particular ire and though it went nowhere it triggered a reaction. In the end the Fire Eaters were blocked at the convention by more moderate factions. There was no rebellion. That had to wait ten years, but in that decade tensions simmered until the election of Abraham Lincoln proved too much for the defenders of slavery to bear.