Sai was originally inserted into Team 7 with a two-sided agenda:
1. Maintain an observational lookout of the Kyuubi jinchuuriki for Root
2. Broker a secret pact with Orochimaru in order to make contact with Sasuke Uchiha and eliminate him
With Danzo's premature demise, Root will have likely been disbanded and Sai would have become an independent agent. He can finally think and act for himself. For the first time in his life, the shaping of Sai's future is up to him alone.
What Sai desires most is probably just the affections of his new "family". After having his humanity and name stripped from him, the most minor of interactions must feel like an exhilarating breath of fresh air to him. He's savouring the bits and pieces of a life that he never had before - connections to people with genuine sincerity in his heart and a sense of belonging which he never had as a Root operative who was passed around from one squad to another while holding to the formalities and discipline of his training.
Unlike Sasuke, Sai wasn't born with a silver spoon in his mouth, both technically and socially. He had to work for every bit of trust and affection received from Naruto, Sakura, and their age group. There wasn't any animosity with Sasuke because everyone admired him and wanted to earn his confidence, even Naruto admitted to such. They all tried to look past the seedy underbelly of his character and look for the brief glimpses of decency that he showed in Part 1 - which have become less and less frequent since he relinquished himself to hatred and negativity.
Seniority. That's really the only argument that Sasuke's position on Team 7 has. Oh, and Naruto's personal crusade to stamp out every inkling related to the "darkness" that's imaginable. There's also that.
When it comes down to it, Sasuke doesn't give a damn about what his "teammates" think, neither does the sanctity of the unit undermine his personal motives for fighting. For the longest time he sought to undo that relationship with his maddened rantings about a genocide to "cleanse" the Uchiha name. And we're supposed to disregard his past actions and treat it like water under the bridge? Compare him, treat him to the person who has wanted to be part of the team and the circle of companions all this time? The person who hasn't shunned their teammates' opinion about himself - who even went as far as to seek information from a book to learn how to care for others and interact with them? Who tries to fulfill the wishes of his friends, for the sake of their happiness, even when it might contradict the pragmatism of his own understanding of such villainous characters?
Personally, the claim for Sai's position on the team is far more worthy and honest than Sasuke's. He's earned that privilege and I would rather see him stay as a permanent member of the squad.
Edited by Atheck, 27 July 2014 - 06:26 PM.