Lulu was actually a criminally nice person as a child, and he's still rather nice deep down in his silly little heart. I'm not sure why fandom wants him to be like Light. Light's sociopathy was fascinating, but it's also one-dimensional. Lelouch is going against his nature with his decisions and delusions, and I think it makes for a much, much more interesting character. Maybe they want him to be smarter? I like his plans being flawed, though. It makes him so much more 17th year old human and not this calculations machine. (This doesn't mean I don't like Light, it's just that Zero is a more multifaceted character than Kira)
Unless she dies. He might really become a monster that way, though I also think he wouldn't ever really become irredeemable.
Re: tl;dr
Unless she dies. He might really become a monster that way, though I also think he wouldn't ever really become irredeemable.