The lingering question is why he did not take the moral high ground and free the slaves in 1861. However, I do not want to continue this debate here - let's save it for a "lincoln" post. We'll focus on secession in this forum.
Lincoln didn't start the war, he just reacted to what the Confederates started. Had he just let the Confederates do whatever they wanted to do, there still would have been a bloody conflict over slavery, perhaps in the form of a guerilla war that lasted for decades and killed millions. In the meantime 4,000,000+ people would still be in bondage -- though apparently their suffering is of little important to you.
Moreover, I don't know where you got your 600,000 number, but battle deaths totaled about 200,000. Arguably, most of those Civil War soldiers who died of disease or other non-battle causes would have done so anyway had there been no war. Almost all of the Union soldiers who died (including my ggguncle) were volunteers, so you can't blame Lincoln for their brave decisions to lay their lives on the line for liberty. The Confederate soldiers who fought willingly got what they deserved for fighting for the slaveholders, and you can't blame Lincoln for the Confederate conscripts who died.
Yes, in the end slavery was ended - but surely there were more effective ways. Don't think Lincoln's way is the right way!
As I stated before, I'm still waiting for one of you Lincoln bashers to explain what you would have done to abolish slavery in a more efficient manner. Keep in mind that Lincoln was even amenable to bribing the slaveholders to free the Negroes they held in bondage, but the slaveholders were a hardcore bunch of lunatics who would have none of that. For them it was a matter of Southern "honor" and "liberty" for them to keep Negroes subservient.
The lingering question is why he did not take the moral high ground and free the slaves in 1861.
I answered that in Number 171 above. Please explain how you would have had him do it.