Many people saying things like "turning good", or "joining the good guys" or "good and evil"... I respect your opinions, but I don't think Naruto has ever been about that. The whole point behind almost all the enemies we've seen is also understanding where they come from. There have been only a few of those whose reasons and background we didn't get to see. Like Deidara, Hidan or Kakuzu... But almost everybody else has got a reason behind their actions, and the whole point of fighting them is showing them how they could have chosen a different path, hence Nagato's last choice to revive everyone, Sasori's last words to Kankurou, Gaara changing and becoming a caring, kind Kazekage...
Orochimaru is important to the story, being Sandaime's apprentice and one of the previous generations' version of Sasuke. Now I'm kinda glad he came back, because now we get to see (or I hope we do) his past and the reasons he is who he is. I hate the fact that fanboys can ruin one's mood when it comes to him and the Uchiha Clan members, but hell, he's interesting. Having him fight alongside the Alliance would definitely be interesting. Only in a temporary period of time, though. He's still got much arrogance to be kicked the hell out of. Just like Sasuke.
If this was a story about simple, absolutist terms like good and evil, then it would be boring. Everybody seems to think Naruto is that simple a Manga... When it's not.
I guess they don't take it so seriously.
