It's still the whole point that Kishi was going for. Gaara, a moral voice of reason also says the same thing to Naruto. Sasuke is the point where the chain could've been broken. After the Kage Summit, who would've really felt so strongly for Sasuke that they would get revenge on the K11? Naruto? Naruto and Sakura are the only people who care about Sasuke anymore and it's not as if they would kill Shikamaru. They'd be a little mad but the cycle would be temporarily over. The entire shinobi world rightfully wanted this outlaw dead
That the entire Shinobi world wants him dead does not justify extrajudicial killings. The reason our justice system guarantees even the worst offenders the right to a fair trial is what is missing in that world, and one of the main causes for the chaos they are experiencing. In a fair trial, Sasuke could have presented as evidence the secret dealings that lead to the Uchiha massacre, the fact that he was going after Danzo, and not the rest of the Kages during that attack, the fact that Danzo in fact tried to break the deal with Itachi (by sending Sai to kill him), and tried to kill him during the fight, while Sasuke was asking him first to confirm what he had heard. Perhaps even use genetic evidence for an insanity plea.
What you are saying is that because the only people who still care for him are Sakura and Naruto (obviously false - add Ino and Kakashi, and his Taka teammates, at the very least), and they are not the vengeful types, then it's perfectly okay to kill him. But a true justice system does not work like that. In the end, Naruto's solution on finding common ground with him and trying to treat his mental breakdown, is the correct action here. The problem can't be solved through logical means, but by giving Sasuke a reason to live beyond revenge.
Sasuke at the Kage Summit was corrupt- he was ready to kill innocent people who weren't involved and therefore any way you look at it- Sasuke was entirely at the wrong. It's one thing killing Danzo. It should've stopped there. Crazy laughing and trying to kill Karin, Kakashi, Sakura & Naruto...his death WOULD'VE benefitted the shinobi world. The only reason they didnt is for the sake of the story and because Naruto has his own resolve.
He was there to kill Danzo and not the others. And the only ones he killed there were Samurai - in self defense after he warned them. I am not trying to justify his actions there, but he is not the monster you try to portray him at - and deserves the right to put his side of the case on the table.