From my experience, the people that tend to hate Luke either A) haven't really played the game or B) are guys.

I see him get bashed a lot at the gamefaqs boards. It seems that a lot of them see Luke's desire to change as nothing but him being emo, lol. Nevermind his emotional growth, he's depressed! How dare he!

Then again, the people on gamefaqs' boards don't have much intelligence to speak of, so... yeah :p Most female fans of the game I know (including myself) looooove Luke. And I don't get how anyone can resist him. He's so adorable! Out of any RPG I've played, I think he's one of the best developed main characters ever. I got emotionally attached, too T___T