Fair enough. And you're right, men fought for many different reasons. Some sought to preserve the Union, others to end slavery, still others were drafted, some responded to the Union's enlistment bonus. Some famous veterans, such as Henry M. Stanley of finding Livingstone fame, fought for both sides (as did the father of the woman who still receives one of the last Civil War pensions).
But Lincoln was a lawyer. Based on Dred Scott he didn't believe he or Congress had the authority to end slavery. The Emancipation Proclamation was an emergency wartime measure which he had no idea was actually legal or not. I think the possibility of black people freed by the proclamation being forced into slavery post-war was what in part fueled the urgency in passing the 13th amendment.
You're right, in part, that many traditional heroes are being re-evaluated. Sometimes wrongly. Lincoln & the men who fought for the Union were all heroes, because even if they didn't fight to end slavery, the alternative would have been to see slavery continue indefinitely & even spread as the Confederacy had plans to expand into the south, Mexico & even Central America, where slavery had been banned.
I think it is heartening to see more people declare that Lee & Jackson, etc. weren't heroes after all, but traitors. If only Lincoln had survived & been able to pursue Reconstruction, along with Sherman's Gen Order #25 (if I have that right), the present day might be much different & far less controversy over the whys & wherefores of the Civil War.