WARNING: the following contains spoilers for My Hero Academia: World Heroes' Mission, now playing in theaters.
The new My Hero Academia movie ups the ante, sending more than half of class 1-A across the globe to confront the villainous Humarise organization, which has the express purpose of ridding the world of Quirks to purify the human race and reset it. The group, including its leader Flect Turn, has cited the Quirk singularity theory as a justification for their actions.
Flect Turn is convinced that Quirks are an illness, and only by wiping them out can the human race restore balance and create a more just society. However, his real motives are more personal than that, and brief flashbacks near the movie's end make it clear why. Flect Turn's personal motives might also remind fans of similar villains such as Himiko Toga and the Meta Liberation Army's members.
Flect Turn Projects His Personal Pain Onto the Globe
At first, Flect Turn presented his Humarise cause as a necessary evil, a bitter medicine to cure an even worse disease, that disease being Quirks as a whole. To some extent, Flect's crusade seems justified, since Quirkless individuals really do struggle in a Quirk-dominated world, and there is evidence that the Quirk singularity really might come to pass. However, Quirkless people are not truly helpless or completely alienated, as Melissa Shield personally proved, and the Quirk singularity is far from a guarantee. It's just a theory, and a theory isn't a good reason to set off bombs filled with the dangerous drug trigger to wipe out 80% of the human race. Flect can't use that theory, or any reason, to justify mass murder like that.
Instead, brief flashbacks during Flect's climactic duel with Izuku suggest that his entire Humarise movement is based on his personal pain. Despite his rhetoric, Flect Turn was born with a powerful Quirk, one that turned his skin blue and allowed him to reflect Quirks and other things back at their sources. It's an effective Quirk for battle, but clearly, Flect Turn never wanted to become a fighter, because he saw his Quirk as a burden and a curse, not a tool to be used. He was alienated by everyone in his family, at college, and in society as a whole. This isolation fueled his resentment toward not just his own Quirk, but Quirks as a whole.
No doubt Flect inferred that many other Quirk bearers also feel rejected or scorned due to their appearance or abilities, and he seeks to purge the globe of Quirks not to benefit Quirkless people, but to end the suffering of people who hate their own Quirks. If he could, Flect would go back in time and be born Quirkless and live the ordinary life he always wanted. If society rejects him, then he will reject society right back, and wipe out the Quirks that serve as the pillars for that unfair society.
Flect Turn & Other Villains Who Seek Freedom From Society's Rules
Flect Turn deeply resents society and feels that he cannot be truly free to live the life he wants so long as society's current rules and norms persist. Thus, he would agree with the ideology of groups such as the League of Villains and the Meta Liberation Army, at least to a reasonable degree. These groups' members feel that society has no place for them, and the strict, hero-dominated world is predisposed to reject and alienate people who happened to be born with the "wrong" Quirks or personalities. They lost the Quirk lottery by having dangerous, strange, or unpredictable Quirks, so these villains banded together to find people who can accept them. These villain groups then seek to overthrow the society that practically forced them into villainy.
Flect is just one of several characters to expressly feel this way. The yandere villain Himiko Toga can't even hurt people with her Transform Quirk, but her fondness for blood and mental instability caused her to be branded as a villain not long after she graduated from junior high school. Himiko mentally reflected how she just wants the freedom to be herself, and she finds it unfair that her parents, teachers, and society deemed her "evil" just for being herself. Spinner and Tomura Shigaraki feel the same way, and so do the many Meta Liberation Army members. They, and Flect Turn, aren't villains because it's fun -- they fight because they were rejected as human beings born with the "wrong" Quirks and attitude. They'll do anything, even set trigger bombs, to make a world where they fit in. If that new world comes at the price of pro heroes and the innocent, then so be it.