WARNING: The following contains spoilers for Attack on Titan Season 4, Episode 26, "Traitor," now streaming on Funimation, Hulu and Crunchyroll.
When Bertholdt Hoover and Reiner Braun outed themselves as the Titans who destroyed the Walls at the start of Attack on Titan, the pair became the outright villains of the series. However, Season 4 has done the impossible by making Reiner and Bertholdt (albeit posthumously) tragic and sympathetic characters. During Season 2, as the duo attempted to flee Paradis Island with Eren Jaeger as their prisoner, Bertholdt made a desperate plea to his friends in the Survey Corps that "someone has to do it." Now, as Armin and Connie are forced to betray and kill their own comrades for the greater good, the import of Bertholdt's tearful words hits harder than ever.
The line between good and evil is blurrier than ever in Attack on Titan as the Survey Corps and the survivors of Marley have banded together to stop the Rumbling. Eren, Floch and the Jaegerists plan to destroy all life outside Paradis Island to ensure the survival of the resident Eldians. Eren's closest friends have agreed that genocide is not only wrong but that it won't help Eldians in the long run to be the only people on an empty planet. The Marleyans, on the other hand, have been trying to stop the Rumbling from the start -- hence their invasion of Paradis Island in the first place.
Unfortunately for the surviving Scouts who hope to stop Eren, the Jaegerists are their former comrades, some of whom they have known since their days in the 104th Cadet Corps. The Jaegerists have let their suffering at the hands of Marley and the general bigotry from the rest of the world toward Eldians consume them. Eren's followers have decided that revenge is the best path to peace and they are willing to lay down their lives for their cause. In their eyes, Mikasa, Armin, Connie and Jean are traitors for trying to stop the Rumbling. The surviving Scouts and the Jaegerists fundamentally disagree on what the greater good is, and as the Scouts are the minority for their stance on the Rumbling, they have been labeled the traitors.
This conflict is heartbreakingly similar to why Reiner and Bertholdt destroyed the Walls in the first place. They were taught that the Eldians on Paradis Island were devils who would destroy the world if they could and that eliminating them was the best course of action to save it. Their mission was to reclaim the Founding Titan for Marley, which is why they kept trying to kidnap Eren Jaeger. At the height of the conflict, Bertholdt tearfully admitted that he truly did think of the Scouts as his friends and it was awful to have to betray them, but someone had to do it.
The true meaning of Bertholdt's words is clearer than ever now; someone has to get their hands bloody if they want to save the world. The Jaegerists are willing to kill to protect Paradis Island, and now the Scouts have found that they will have to do the same in order to stop the Rumbling. Reluctant to attack their former comrades at the port, Armin and Connie attempted a ruse to acquire the flying boat without any bloodshed, but Floch and the Jaegerists did not take the bait. Flashing back to Bertholdt's plea, Armin has realized that now he's no different than Bertholdt was back then. Just as Eren admitted he and Reiner were the same when Eren attacked the Liberio Internment Zone, there's no path to peace without bloodshed in a world of Titans.
Diplomacy has well and truly failed in Attack on Titan, and now it will be a fight to the death to stop Eren from destroying the entire world. Even the meek and quiet Bertholdt Hoover could stick to his ambitions at tremendous personal cost, and now Connie and Armin have been forced to do the same as Connie tearfully killed two of his oldest comrades. Floch might just be a psychopath, but the majority of the Jaegerists only want Paradis Island to be safe, no matter the cost. Whether the Rumbling succeeds or not, things are only going to keep going from terrible to unspeakably worse on Paradis Island as Attack on Titan continues.