There are, as people may know, definite differences between 'Evil' Damon, and 'Evil' Stefan. These differences relate mainly to the ways in which they were turned into vampires, and why, in my opinion.
Damon, as we know, lost all hope when he assumed that Katherine had died, but he also felt the sadness that he felt that Katherine and Stefan had betrayed him. Katherine, because she turned Stefan, and Stefan, because he loved Katherine, and Damon was not happy about that.
Stefan killed their father, Guisseppe, then forced Damon to join him, in becoming a vampire as well, wheras the broken hearted Damon only wanted sweet oblivion after being betrayed by his own brother.
So, here we come to the crux of the differences in evil. Damon, after vowing to make his brother's life a misery, went off and embraced his dark side, killing many helpless victims, just to survive. There was no joy in killing for Damon, it was a means to an end, until he met Sage, who introduced him to the fact that being a vampire could have sexy side fringe benefits.
After losing Damon, Stefan swore off blood for a time, feeling an enormous sense of guilt for killing his father, and dragging Damon into what he saw as a cursed life. Poor Stefan. He hardly realised that by denying the dark needs in his nature, he became a blood addict, addicted to the merest taste of human blood. Damon, alternatively, was able to have some restraint when need be.
Stefan became a 'ripper', ripping people apart, and in remorse, trying to put them back together. Classic addiction.
So, Stefan DOES have a far more evil side to his nature. Damon can be redeemed, wheras Stefan as an addict, must always be vigilant, lest he snaps.
I cannot justify allowing Elena to form a serious attachment to someone who has an evil alter ego bubbling below the surface of his psyche. He will always need a sponsor- perhaps his own brother Damon, to keep him from being tempted to give into his baser urges.
Damon's 'evil' is one of impulse control- he doesn't think before he acts. He is emotional, volotile, passionate. However, I feel that Damon CAN be redeemed with the right motovation, he just needs to want to change, be a better man, and he can be.
Anyone else have any thoughts?