keep your powder dry
It is my opinion that he made lasting contributions to the US as well as inflicting lasting damage. I do believe that he saw the damage he did as regrettable and undertaken only under necessity - I do not believe that he wilfully did mischief for its own sake.
An added problem is that far too many of the "Lincoln as saint" partisans have a thinly-disguised, self-righteous hatred of the South as a cultural entity.