“It is all my fault” - Gen Robert E Lee, upon being notified by Major Pickett that he “had no more men.”
“Joining the military was the worst decision of my life” - Gen Robert E Lee
It appears that Gen Lee’s own opinion of his prowess was somewhat more circumspect. The deaths of his own (and likely, the Union’s men) weighed heavily on his soul in his last years. He threw in his lot with the rebels and fought in a cause that was evil and unconstitutional. A half a million men (and who knows how many civilians) died as a direct result - and his prowess as a general prolonged the suffering. He was in the end, a tragic figure, but deserves no sympathy for his role in the Civil War.
Lincoln, OTOH, had done NOTHING (other than win the election of 1860) that would justify Southern secession. In fact, HE WASN’T EVENT PRESIDENT YET WHEN IT OCCURED!! (He took his oath in March 1861, months after the Southern states voted to secede.
He had no choice but to fight to save the Union against the Secessionists. To do anything else would have been an abrogation of his OATH of office.
Defending your homeland from an attack by a powerful slave owning nation like the USA is not evil. It is the most honorable thing you can do.
And the US Constitution said nothing on the subject. The Declaration of Independence (which is the mother of the US Constitution) says all that needs to be said on the subject.