Elaborate, please.
I by no means consider myself an expert, but I am fairly well read on the subject of the Civil War and Lincoln. From what I have read, Lincoln believed that slavery was a moral wrong, but he felt that he could not, as President, lawfully remove slavery from the South - only Congress could do that. Lincoln stated this several times during the Lincoln-Douglas debates.
What pushed the South over the edge (in my humble opinion) to withdraw from the Union was Lincoln's opposition to slavery being introduced into the territories. They knew that new states were going to be added - if none of these came in as slave states, then the balance of power between the slave states and the free states in Congress would be upset.
Lincoln believed in states exercising their rights as permitted in the Constitution, however, he did not believe that states could merely vote themselves out of the Union whenever they felt like it. Lincoln believed that secession, as preached by many Southern politicians of his day, would lead to the ultimate destruction of the United States as a nation. I think he was right. I believe that if Lincoln had allowed the South to secede as they did, we would not just have two nations here, but several.
Even some of the Southern states threatened to leave the Confederacy when they got upset with the Richmond government. Once the principle of secession, as practiced by the South, was permitted, then what could a national government legally do to prevent each individual state from seceding at one time or another as they saw fit?
Think about all the times in our history when one state or another was ticked off at the Federal government - heck, I've wanted my own state to secede myself!! If secession was legal, we would be a bunch of separate countries today - not the United States.
Lincoln did what he felt he had to do to save the idea of United States. Remember we weren't even a hundred years old at that time. Secession, as espoused by the South, was a direct threat to our existence as a country.
Let me qualify that I do believe that the people have the right (and the duty) to change the government if it no longer fulfills its duties to protect the rights of its citizens. The Declaration of Independence expressly states this fact. However, as long as we have the possibility to peaceably change the direction of our government through Constitutional means, I do not believe that secession is an option - yet.