Yeah, well the problem there is that the slaves were not freed until long after the war was started. Hence Lincoln's letter to Greeley http://www.abrahamlincolnonline.org/lincoln/speeches/greeley... wherein he writes '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.'

The South went to war not because the slaves were going to be freed, but because Lincoln did not agree with Slavery as a moral good.

As per the Cooper Union address: http://www.abrahamlincolnonline.org/lincoln/speeches/cooper.... where he said 'what will convince them? This, and this only: cease to call slavery wrong, and join them in calling it right. And this must be done thoroughly - done in acts as well as in words. Silence will not be tolerated - we must place ourselves avowedly with them.'