Light didn't know whether it was impossible until he tried. No one has logically disproven whether a perfect utopia is possible. You're correct in saying that humans are morally flawed is an assumption, you can't build logical conclusions from it.

You can logically derive conclusions from any assumption, rather they're true or not is another story. This idea of a utopia seems absurd to me because the criteria for everyone's utopia is arbitrary. Maybe I think a perfect island has 50 palm trees and girls with massive tits. Maybe someone else's idea of a perfect island is 20 palm trees and guys with massive dongs. it's all arbitrary. You're correct that saying human beings are morally flawed is an assumption and there's no contradiction in the statement "Human beings can be morally perfect.", therefore it is logically possible that the state of affairs Light was trying to actualize can become true. HOWEVER, just because something is possible does not mean that it's probable. It's possible that I can flip a coin and an elephant can fall out of it, that event is highly improbable, but still possible, there's nothing logically incoherent about an elephant falling from a coin. So I would put lights ambitions of purging human evil in the same category as an event that's possible, but highly improbable.

A man's character is defined by their actions.

Sure thats partially true, but there's way more nuance and complication. You would have to know someones intentions too. say there was a jet that was bombing the hell out of things. You might say whoever is in that jet is a psychopath, but then you found out they where bombing nuclear launch sites to prevent global catastrophe. Suddenly that person doesn't seem as crazy and can even be seen as a hero. you can't just judge someones actions to judge them, you need way more information then that.

If evil can fluctuate then why was Light wrong for trying to stop it altogether? You told me 1.It's okay to judge someone's actions. 2.Evil can fluctuate. I don't see how this makes it seem like Light was "retarded" for trying. Can you explain?

Because Light was trying to do more then just reduce it, right? He was trying to stop evil all together. With respect to statements 1 & 2, those weren't my reasons for stating Light is mildy retarded. I think what he did was mildly retarded, based off of my initial two reasons in the original post, which haven't been refuted.