I agree that all of the characters are flawed and I love that, no one is perfect, this is noir. The problem with Duncan is that he is not human or sympathetic and the narrative constantly treats him as such. And Logan did not blame Veronica for what her father did, he blamed her for supporting her father's actions. It's not defense mechanism for himself, it's misguided protection of Kanes and it was horrible, not just unfair. The difference is that Logan is great friend to Duncan and Duncan just doesn't care. Is such a problem with both writing and acting that Duncan seems more like an alien trying to learn to imitate human emotion. The acting is wooden but he is also given such a strange emotional beats to play, like this one with Logan. He has no emotional or logical high horse to stand on(or excuse), he abandoned his best friend in his time of need and then came back to town and didn't even call him but instead went to stalk his girlfriend at her place of work for the purpose of convincing her to break up with Logan.
Repeating what I said in the topic for last episode, this both show and viewer tendency to dismiss Duncan as benign boring person is so dangerous to me when I think about teenagers watching this show. The rape storyline made him a rapist(I believe not on purpose but implication is there when you put together facts of the night) but instead we are supposed to believe they just had "perfect" first time Veronica just can't remember. He literally stalks her but we are supposed to think it's romantic and sweet. He breaks up with her by ignoring her and not giving her a reason and we are supposed to believe it's justified, it's not BTW. Duncan acts as classical narcissistic abuser there, Veronica is not a person, she is thing and her emotions don't matter. Only him avoiding discomfort is important. He lies to her, dismisses her and patronises her and cheats on her(I'm calling death of an author on this one, the storyline just doesn't make sense if he didn't cheat on her Rob!) and the narrative frames it as normal and understandable. I don't mind toxic, abusive characters. I don't even mind toxic, abusive ships but please, acknowledge the wrongness in the narrative.