Judging from the changes in Onoki, I'd say that Gaara has learned or is on his way to learning the secret of Naruto's Therapy no Jutsu. Sadly, Sasuke remains immune to the effects no matter who's using it. And you know what? As with Jitters, I am prepared for any flames that might come.
As ever, unreliable narrator is in play; try to think about what Gaara knows of the situation and about how his own personality and experiences would play into his interpretation of things. Gaara believes Sasuke is irredeemable; he's the one saying that here, not me.
I own nothing.
"If you really count yourself as Sasuke's friend, think hard about what you must do."
Naruto shakes him off and makes it clear and well that he doesn't accept a word out of Gaara's mouth, that he's not listening to a word he says. You're wrong; you're misguided; you're crazy; you're too stupid to see it my way. Naruto might as well be saying that and Gaara, with his hard-earned patience, does not respond.
Gaara knows better then to try to argue with Naruto when he's determined on something.
The air here is so cold, and Gaara holds his scarf up closer to his face against the wind as he and his siblings start to make their way back south. They travel and silence and every once in a while Temari and Kankuro shoot apprehensive glances at him. They've long since figured out not to interrupt Gaara when he's brooding.
Naruto…
You know the Uchiha Sasuke who was a genin of the Leaf. You know the Sasuke who trained with you, taunted you, defended you even when he didn't want to.
I don't think you've ever met the Uchiha Sasuke of the present.
Thinking hard, the brow of the young Kazekage furrows, heavily distorting the Ai scar over his left eye. His hands are chapped and cold and Gaara's fists clench to give his fingers some warmth.
Naruto's not seeing it. Naruto, with all his impossible hope and determination, still thinks he can save Uchiha Sasuke. It's admirable; it's incredible. It's this very hope and determination that pulled Gaara from darkness devouring, and he will never stop being grateful to Naruto for that.
You hold me up as an example. You look at me and say "If I can save you, I can save anyone" as though I was the lowest of the low when you met me. That in itself is fallacy; I was steeped in sin and mire and you waded in after me to pull me out. I was drowning and you put air back in my lungs. There are those who were worse than me though; don't ever assume that I am the greatest challenge you will ever face.
I don't think you can do for Uchiha Sasuke what you did for me though, Naruto. I don't think anyone can, not anymore. I was dragged into the darkness, but Sasuke, he walked in. He went in willingly, and you won't be able to bring him out into the light of day.
Still Naruto protests that Sasuke can be saved; still he says that the Uchiha can be reached. Gaara begs to differ, and wonders in earnest What could I say to make him see? Uchiha Sasuke fought like a man possessed, howled like a rabid dog. He said that no one could ever understand him and that to even try was blasphemy.
Even if he could be saved, Sasuke won't be coming home. It's not that simple; it's never that simple. Every country on the continent wants his head, including Hi no Kuni; Sasuke won't be coming home.
He can't be saved. He doesn't want to be saved; he has to want it first, Naruto, why can't you see that?
It's not nearly as simple as Naruto makes it out to be. The whole "Uzumaki Naruto insists that Uchiha Sasuke can be saved and anyone who doesn't believe it is blind" argument Naruto lays forth would be fine and well if Sasuke wanted to be saved and the five nations plus the Land of Iron didn't want to make the Uchiha clan extinct once and for all. Gaara knows with a politician's eye that this is a complicated mess, a Gordian knot that can't be undone.
Gaara can see how this will play out. It's sad—Sasuke had so much potential and for a time it looked like he'd be able to shake his past—but it's the only possible outcome he can imagine.
Sasuke will be killed, if not by one country than by another. His corpse will be displayed in a visible place to show what becomes of those who have no loyalty to anyone but themselves. After his corpse is so thoroughly rotted as to be unrecognizable, it will be dumped in a potter's field without ceremony, and forgotten. If Sasuke is ever spoken about, it will only be a teacher at an Academy warning children that allowing the thirst for revenge to overtake you will make you a degenerate like him. Parents might whisper to naughty children "Be good or Uchiha Sasuke will come to kill you in your sleep!" like he's some sort of bogeyman.
If Naruto can't see it, then he is without a doubt the blindest man Gaara has ever known, and this is even more sad: the man who saved Sabaku no Gaara, believed by all to be irredeemable, can't save Uchiha Sasuke and can't save himself.
Sasuke will devour the world, Naruto. He will kill you at the last to show you what he has done, and if then your eyes are not opened to the reality of him, then I can only assume that this will be because Sasuke plucked them out earlier for safety.
It's sad, but the only solution Gaara can find to this problem is for Sasuke to be killed. Only then will he cease to be a threat, because even if Sasuke was redeemed and the five nations and the Land of Iron agreed to let him live, no one would ever trust him again. There would always be the ANBU details, the restricted freedoms, the mandatory meeting with a Yamanaka to search his mind for the seeds of treachery. Tsunade would take one look at Sasuke and think, even if she didn't allow her Senju ancestry to cloud her mind, Once a traitor always a traitor.
It's what everyone would think. Even Haruno Sakura, a girl who Gaara knows well to have some sort of romantic attachment to the Uchiha, would have to see it. She's clear-headed and intelligent; she'd see the threat he poses.
Everyone would see it but Naruto himself.
It's sad. It's heartbreaking.
Gaara knows the truth, but he can't make Naruto see it.
Sasuke has nothing to return to. He isn't coming home.