It feels like the common thread is "I'm a major bad guy in Naruto, I lose/die, then I have a change of heart and want to help Naruto once bigger baddy shows up". When does a bad guy remain a bad guy? (e.g. - Zabuza, Gaara, Itachi, Nagato, Orochimaru, Kabuto, Sasuke, Obito, and the demon fox who was supposed to be the incarnation of the world's Malice/Hatred).
Even Madara seems poised now for a return as a good guy since there's a bigger threat and he originally had good intentions when he was a kid.
Is there a reason for this? Why aren't the bad guys more angry that they lost, and join up with new bad guy? Seems like they give up really easily and have no commitment to their goals.