Lincoln's decision to ban slavery was politically motivated by the Civil War. In his early career in political speeches, he made statements that stated he did not believe whites and blacks could not live together. In the White House, he was in favor for quite some time not for emancipation but for shipping blacks back to Africa instead. Part of these feelings of his are just a reflection of the time. But he isn't the great black protectionist he is portrayed as. He also violated the Constitution while in office - he closed newspapers in the North that printed pro South editorials and he imprisoned politicians that disagreed with him.

Lincoln actually wasn't a good president anyway. Regardless of his slavery ideas.