WARNING: The following contains spoilers for Attack on Titan Season 4, Episode 17, "Judgment," now streaming on Funimation, Hulu and Crunchyroll.
Things have not gone well for the Survey Corps in the first episode of Attack on Titan's Final Season: Part Two. After having their trust in Eren shattered in the season's first half, the remaining members of the Survey Corps were forced to decide if they're going to help Eren survive Marley's surprise assault. Despite being freed by Onyankopon, the gang didn't rush to Eren's side as they so often have. The Survey Corps have been completely fractured by Eren's betrayal, and now that the final battle is here, they had to pick a side first.
When Eren forced the Survey Corps' hand earlier in the season by infiltrating Marley alone, forcing them to rescue him, Sasha was killed and Paradis Island became the enemy of the entire world. As if that weren't enough, Eren later beat Armin to a pulp after telling Mikasa that she is no more than a mindless slave whom he has always hated. Suffice it to say that the gulf between Eren and his closest friends is massive, and it speaks volumes that saving his life is something they stopped to debate first.
As far as anyone knows, Eren has thrown in his lot with Zeke and Yelena and is working toward their goal of "Euthanasia" for the Eldian people, aka the population of Paradis Island. The goal is to use the Founding Titan's powers to sterilize Eldians so they can no longer bear children, which means their entire race will slowly die out, ending the threat of Titans once and for all. As this would leave them defenseless as their race dwindles to a handful of the elderly in the future, Eren may unleash the Rumbling, freeing the millions of Colossus Titans within Paradis' Walls to trample the world, so that no country will have the time or ability to attack Paradis Island.
Connie, sick and tired of being betrayed, was incensed by the idea that he has to go fight for such an awful plan thought up by people he hates. Jean agreed that supporting Eren would mean allowing the Euthanasia Plan to happen -- something he isn't too keen on happening either. While Mikasa still wanted to help Eren despite being heartbroken by her last encounter with her foster brother, she was unsure if helping him is what she truly wants or if she's just the slave he claims her to be. Everyone now has a very complicated relationship with Eren, and it could be disastrous if they let their personal feelings affect them on the battlefield.
Fortunately for Eren, Armin intervened as the sole voice of reason, apparently the only one who remains capable of thinking about Eren and the situation objectively. Armin asked his friends if they really believed that Eren wants to take away their ability to reproduce, deeming the notion as outrageous. Armin reminded everyone that Eren, and Eren alone, has the ability to command the Founding Titan, meaning that there's no reason to believe he'll actually carry out Zeke's and Yelena's plan. Eren has been marching to the beat of his own drum all season, so Armin might just be onto something by suggesting he might have no intention of obeying Zeke and Yelena for much longer.
As horrific as it sounds, the group agreed that Eren activating the Rumbling is Paradis' best chance at survival. Having decided to give Eren the benefit of the doubt, the last remaining members of the Survey Corps choose to help Eren unlock the Founding Titan and hope he doesn't follow through on Zeke's plan. If Eren has had his own plan this entire time, it would make more sense that he has been pushing away his friends, trying to ensure that the world's ire will be focused on him, not them. At the moment, Eren could certainly use his friends' help, as he and the Jaegerists are currently having their heads handed to them by Marley. While Mikasa, Armin, Jean and Connie hardly seem like enough help to turn the tide, this group has pulled off the impossible before.