That is not true.
The Corwin Amendment stated that Congress could make no laws interfering w/ the domestic relations, ie servitude, w/i any state. In those states where slavery was illegal, it would remain illegal.
Its only trope to slavery was to re-inforce the Dred Scott Fugitive Slave Law, which Lincoln openly recognized as constitutional law.
The remainder of your post, while more or less accurate, is distorted by this untruth.
The Crittenden Compromise related to the expansion of slavery into the new territories opening in the west, primarily by extending the line established by the Missouri Compromise. Lincoln was opposed to the expansion of slavery into new territories. In any case, none of the 6 articles of compromise entertained the universal application of slavery.
What this episode actually demonstrates more than anything else was Lincoln's desparate attempt to prevent the coming war. By moving, or so he thought, slavery off the table he hoped to diffuse the secessionist movement.
Alas, the southern firebrands were intent upon secession and if necessary, war.
Sources:
Miller, WL, "Lincoln's Virtues", Vintage, 2002, p. 435
Donald, DH, "Lincoln", Simon Schuster, 1995, p.268
Barrett, JH, "Life, Speeches, and Public Services of Abraham Lincoln", Moore, Wilstach & Baldwin, 1865, p. 200
Specifically, the wording of the Corwin Amendment was:
"No amendment shall be made to the Constitution which will authorize or give to Congress the power to abolish or interfere, within any State, with the domestic institutions thereof, including that of persons held to labor or service by the laws of said State."
Upon a critical reading you will note that it forbade Federal interference in states with laws holding people to service.
Your comment that it did not legalize slavery everywhere was fallacious. Here is what you said: "In those states where slavery was illegal, it would remain illegal."
That is on its face not true. The amendment said no such thing.
In ratifying this Amendment, any prohibitive legal consequences for its practice were forbidden.
Thus it remained an option for each state to determine that issue themselves without fear of prohibition.
Should any state decide to reinstate slavery, as it could do so freely, then the Federal government could not interfere.
Simply put, if Indiana or Oregon decided by state law that wanted to reinstate slavery, then according to Corwin, there were no Federal regulations to deny that right.
More importantly, it is quite clear that Lincoln's alleged morality was mitigated by his need for political survival of the union.