I think that what they were going for is that Lucian was someone who looked at the bigger picture. He felt that Damian didn't NEED to be killed per se so he didn't, and that made him weak. In DOS2, he appears to be dead but actually isn't, working to repair the mistakes of the gods and his own. I think he feared the Black Ring and their potential so for him to lay waste to the elves was worth it(again a weakness shown through his own selfishness) and now feels that even if you killed Alexander, that's okay because he feels that its more important to right the wrongs of the Seven and fix the fabric of the veil than it is to do anything else. He can certainly be benevolent and kind, and when I met him in DOS2 he didn't strike me as cruel and apathetic, rather he was more deeply concerned with the greater threat. He knows you did what you had to do to get there. Lucian killed the other godwoken because he could not let another come to the powers of Divinity, lest all the work he did be for naught. He even mentions that he tried to be merciful in his killing.
The overarching theme of Lucian in all games is that he is a "Mortal" given godly powers. The theme of the games however, is that no "Mortal" should have that kind of power since people are selfish and make mistakes. Even the so called "Gods" aren't up to snuff, why would a human man?
If I remember right on my first playthrough (still on my 2nd), Lucian regretted his actions with Damian, saying it was a mistake, and also regretting his decision on the use of Deathfog with the elves and the Black Ring, and this was his way of "redeeming" himself. Although his logic is flawed because the elimination of all source would render him mortal again, and thus, open to invasion from Damian, and the fact that he can actually die. I can't imagine the pandemonium that would be wreaked if Damian were to invade against a mortal Lucian and kills him publicly. (Although it'd be an epic game to see for a 3rd installment). I agree with his decision that the God's had to be taken care of after revealing their true parasitic nature, however, his elimination of source is nothing short of brutal. I feel like Lucians decision overall is simply short sighted, and his guilt is overriding reason.
Despite all that I've said about Lucian and his guilt over his decisions, I want to say that were seeing a Dr. Manhattan version of Lucian, where he's more or less detached from human emotions and thinks on a grander scale that people cannot comprehend.
