There is no need for Kira to develop any further, he has reached his potential as an individual. Kira is the way he is because he did kill people, though he didn't want to; he was forced to walk down a path he did not choose, rather it was forced upon him under circumstances; he did not see the point in war and fighting, he had to find some meaning to all the madness going on in the war; he lost people he cared about though he tried to protect them, that is why he protects everyone now. Think of it like this, Kira reached spirtual enlightenment (like the Budha) after he ended up with Lacus. While with her, he lost his will to fight. However, after losing his will he regained it with a purpose, to protect. Now hating on Kira is like hating on Jesus for the way he was, it just doesn't make sense. I understand not everyone thinks alike, further not everyone can understand such concepts or believe such things as enlightenment, but there are those who do and have experienced them. So KIRA is the best, and that is all there is to it. I believe Shinn might reach a point of enlightenment as well, but who knows with the amount of episodes that are left.