[quote="FriendlyHyena"]I don't know what Zira did, but if it was something as petty as disagreeing if Scar was good or bad, Simba seems as bad as his uncle in sending the young cubs Kovu, Vitani, and Nuka to the Outlands like that. What did they do against him?
Again, Simba kicking them into the Outlands gave them a PERSONAL reason to hate him, just like Scar sending Simba into the Outlands for years increased his hatred for Scar.
Also, more to the point, he seems merciful enough to have let his uncle who had
1.) Admitted to murdering his father
2.) Just pimp slapped his mother.
3.) Mismanaged the Pridelands and been about to have them be stuck there with no food due to his own stubbornness.
4.) Had just tried to murder him as a cub and then recently as an adult
5.) Had lied to him and made him feel guilty for years for his own father's death and had told him to leave the Pridelands where he nearly died in the desert.
6.) Had, in the musical and the cut movie, tried to make Nala his queen by force
leave the Pridelands alive, then why didn't he cut Zira's cubs any slack?

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We're not certain but it's possible leaving Scar alive wasn't mercy. Simba has never gone for death his punishment is always exile. It's possible Simba uses exile as a means of revenge rather than mercy he's not willing to get his paws dirty but he wants to see those who wronged him pay, so he exiles them.
Exiling Scar might not be an act of mercy it might just be Simba putting Scar through everything he went through as payback after he's dead Simba feels Scar didn't pay enough for his crimes against him and his loved ones as well as his home and as such extended his wrath to his family because they obviously must be just like Scar and deserve the same punishment.
This fits how he regards Kovu in SP and even the outsiders he just sees all of them as extensions of Scar it doesn't matter how old they are he won't allow Scar's legacy to exist in his kingdom. How does this make him better than Scar it really doesn't, Zira's vendetta is the judgement Simba brought on himself much like Scar brought about his own judgement.