Dive into your creative stream
i wish people didn't try to filter geto's decision through a western lens because they're forgetting a huge part of the puzzle and it's the fact that sorcerers are oppressed by non-sorceres in the world of jujutsu kaisen. geto’s whole thing is "there's so few of us and yet we work ourselves to death for your peace of mind, while you remain ungrateful".
it's all more equivalent to health care workers trying to treat a virus. which also aligns thematically with the subject of labour across the series (jujutsu sorcerers being spread thin to the detriment of inexperienced workers, a job you value vs a job that compensates but drains you of your spirit, the myth of meritocracy) .
which is why controlling the output of cursed energy should be seen as the equivalent of being born with or developing an immunity to a disease. this is why a "culling" sounds possible to geto to begin with— people being pushed to adapt or die in their lifetime to prevent future outbreaks, like one would with a virus. strongly differing to kenjaku, because they essentially yearn for this disease to spread out of morbid curiosity (while geto wants the work to end):
geto is a character you are meant to see yourself in. as, in all likelihood, a laborer yourself or someone that will become one. his story is that of exploitation at the hands of a system that only cares for results. leading to isolation in hopes of achieving high productivity.
tangentially, i think a subject that is often ignored in these discussions is the financial incentive to take on more and more work onto your plate too. mei mei is perhaps the clearest example of this, no explanation needed. nobara, a second, when she explictly tells us sorcerery work is the only way a small town girl like her can make it in the big city. megumi, a third, when we learn the money the school gave him helped keep him and his sister tsumiki afloat.
while gege does not delve into geto's past, we can safely speculate part of the reason geto keeps working day after day, after day— despite his wavering convictions is because there is something that encourages him to do so. financial stability would not be an odd motivater. after all, why do we push ourselves everyday to work jobs that no longer add anything meaningful to our lives? geto is the type of character that forces us to examine such things.
as an aside, when he first dons the robes of a cult leader, money is at the forefront of his concerns. if it wasn't obvious before, gege tells you again— choosing not to be a sorcerer, implies a serious loss of income.
i think, all in all, geto's spiral does not hinge on the fact that he was secretly evil the entire time. it lies in disillusionment of a system that only seeks to preserve itself. note that this is why yuki works outside of it. no doubt her experiences as a former star plasma vessel informed her reasoning. it's also why gojo decides to become a teacher and change the institution from within, wielding his privilege as a shield over others.