Your absolutely correct that Lincoln hated slavery and from all indications he had despised it from a young age. However as President his duty was to preserve and protect the constitution, which meant suppressing the rebellion.
These neo-confederates always try to paint Lincoln as some sort of racist. One of their favorite attacks is this letter to Horace Greeley from Lincoln, but for some reason they always leave off the last paragraph. That paragraph shows that Lincoln's position on slavery was morally superior to any of the leaders of the pretend confederacy, and also many northern leaders.
Executive Mansion, Washington, August 22, 1862.
Hon. Horace Greeley: Dear Sir.
I have just read yours of the 19th. addressed to myself through the New-York Tribune. If there be in it any statements, or assumptions of fact, which I may know to be erroneous, I do not, now and here, controvert them. If there be in it any inferences which I may believe to be falsely drawn, I do not now and here, argue against them. If there be perceptable in it an impatient and dictatorial tone, I waive it in deference to an old friend, whose heart I have always supposed to be right.
As to the policy I "seem to be pursuing" as you say, I have not meant to leave any one in doubt.
I would save the Union. I would save it the shortest way under the Constitution. The sooner the national authority can be restored; the nearer the Union will be "the Union as it was." If there be those who would not save the Union, unless they could at the same time save slavery, I do not agree with them. If there be those who would not save the Union unless they could at the same time destroy slavery, I do not agree with them. My paramount object in this struggle is to save the Union, and is not either to save or to destroy slavery. If I could save the Union without freeing any slave I would do it, and if I could save it by freeing all the slaves I would do it; and if I could save it by freeing some and leaving others alone I would also do that. What I do about slavery, and the colored race, I do because I believe it helps to save the Union; and what I forbear, I forbear because I do not believe it would help to save the Union. I shall do less whenever I shall believe what I am doing hurts the cause, and I shall do more whenever I shall believe doing more will help the cause. I shall try to correct errors when shown to be errors; and I shall adopt new views so fast as they shall appear to be true views.
I have here stated my purpose according to my view of official duty; and I intend no modification of my oft-expressed personal wish that all men every where could be free.
Yours, A. Lincoln.
“I understand a proposed amendment to the Constitution—which amendment, however, I have not seen—has passed Congress, to the effect that the Federal Government shall never interfere with the domestic institutions of the States, including that of persons held to service. To avoid misconstruction of what I have said, I depart from my purpose not to speak of particular amendments so far as to say that, holding such a provision to now be implied constitutional law, I have no objection to its being made express and irrevocable.”
I believe it is possible that Lincoln could have been involved with drafts of the Corwin Amendment, but he most certainly was not the author of the final version as he he plainly states he has not seen it. I opted to go with what Lincoln plainly stated rather than pursue the man with the Lamp down some dark back alley of obfuscation. The man with the Lamp is obliquely claiming that Lincoln lied in his First Inaugural.