The following content will contain spoilers from My Hero Academia, Season 6, episode 18, currently streaming on Crunchyroll. One For All came face-to-face with the deadly duo in Season 6, episode 10, giving them a first-hand account of the imbalanced power dynamics and clearly strained relationship between All For One and Shigaraki. Since then, the big debate between One For All Users seems to revolve around Shigaraki's fate, and whether or not he is a hopeless cause.
One For All's Users seem to be divided on opinions; Nana Shimura obviously has personal stakes in the matter, but even she seems to believe that her grandson is a lost cause. Furthermore, All For One has attempted to steal One For All on two separate occasions (targeting En and Lariat in particular) and, after he failed to defeat All Might, the time has now come for Deku to face the music as the next target on the Symbol of Evil's radar.
The Lesser Of Two Evils
Nana boldly questions Deku's ability to kill her grandson, as the traditional capture and arrest procedure no longer seems to be on the table. The rest of the Users disagree with Deku's assessment of the situation, refuting the claim that The Symbol of Fear desperately needs help. They don't deny that Shigaraki is likely uncomfortable being All For One's puppet and possibly wishes to regain control, but that doesn't automatically make him a victim. After all the horrendous things he has done in the past, it's difficult to believe that the boy has suddenly turned over a new leaf. Wouldn't they just be freeing another tyrant by intervening? The lesser of two evils may be to let the villains fight it out among themselves, while One For All destroys two birds with one stone; so long as Deku can deliver the deadly blow.
Daigoro Banjo seems to speak for all the Past Users when he declares that there is nothing but hatred in Shigaraki's eyes, suggesting that his killer instincts are still fully intact, despite his desperate circumstances. Shigaraki went through years of conditioning and has spent the majority of his life under the Symbol of Evil's influence; just because he isn't satisfied with the current power imbalance, doesn't automatically make Shigaraki a good guy all of a sudden. Twice, Dabi, Himiko, Spinner, and the rest of the League of Villains have also had their struggles; however, redemption is met through pure intentions and honorable actions, which many Villians lack.
All For One is fueled by Shigaraki's deep-seated rage, and is all the more potent as a result; potentially powerful enough to finally take One For All down, for good. Similarly, One For All's source of strength essentially stems from their combined willpower, which has often given them the upper hand over their nemesis. The Users, therefore, need to all be on the same page to ensure One For All is running at maximum efficiency. Even Nana is seemingly on board with her grandson's annihilation, stating that:
"There is no way to forgive or understand him anymore...If someone looks like he's asking to be saved, is someone who is irredeemable, do you have the resolve to stop him, even if you have to kill him?"
However, Deku and two Past Users (the Second and Third) won't willingly participate in this murderous scheme.
An Optimistic Approach
In stark contrast to the general consensus, Deku insists that he felt a strong connection to Shigaraki during their otherworldly encounter in Season 6, episode 10, and he could sense how his rival was truly feeling at that moment. Beneath the depths of Shigaraki's hated lies a tear-stricken young boy who is overwhelmed by sorrow and wants nothing more than to be accepted. Deku argues that each Villain's origin story is of vital importance, because if the root of evil can be weeded out, the misunderstood miscreant has a greater opportunity for redemption, and the need for violence may subsequently be eradicated.
To drive his point home, Deku implies that killing Shigaraki equates to stooping to the same level as him, and One For All doesn't exist to end lives but save them instead. This does not dismiss all the trauma and bloodshed that Shigaraki has caused, however, adopting the same homicidal attitude as their nemesis isn't the only solution. Two wrongs don't make a right, after all, and Heroes are not Gods; they shouldn't get to decide who lives or dies.
The Plan Of Action
Although still technically in his early days of Hero training, Deku has decided to cut ties with U.A. High School for the time being, and embark on a solo mission to save Shigaraki and eliminate All For One; hopefully in that order! Who knows, Deku may be able to convince Shigaraki to team up with him temporarily, and aim his anger toward the more deserving target of All For One, the man who ruined his life. There is chatter among Manga enthusiasts that Dark Deku's arrival is on the horizon, which adds an interesting twist to the narrative (the details of which will not be divulged to avoid spoiling the anime-only fans' day!)
Considering Deku's anti-violence approach to the matter, he will likely attempt to subdue All For One (probably with Blackwhip) and find a way to communicate with Shigaraki, pulling off one of his iconic heart-to-hearts and hopefully swaying his rival away from the Dark Side. Sounds like an awful lot of 'ifs and buts.' Yoichi is quick to point out that they will need all the past Users' cooperation if they have any hope of success, and the Second and Third Users' lack of interest sets a rather foreboding tone. The pair seem so averse to the concept of teamwork that they aren't even willing to look at the others, never mind offering up their Quirk's powers (Gearshift and Fa Jin, respectively) for Deku to utilize. They either need to find a way to convince the unaccommodating Users to contribute to the cause or find a way to work without them.