Moral Event Horizon / Fullmetal Alchemist

Ed: Oh, yeah, I figured it out; you did it again! Two years ago, it was your wife; this time, you used your own daughter and her dog to transmute a talking chimera! You can only do so much with animals, after all! It's much easier when you start with a human; ISN'T THAT RIGHT?!
Tucker: I don't see what you're so upset about. This is how we progress. Human experimentation is a necessary step. I would think a scientist should understand...
Ed: SHUT UP! Do you really think you can get away with this?! Messing around with someone's life like that! YOUR OWN DAUGHTER!

Moral Event Horizon in this series.

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• Both versions:
  • Shou Tucker is so twisted that he turned his own five-year-old daughter Nina into a chimera by fusing her with their pet dog Alexander, creating a horrible abomination whose entire life consisted of pain that would later have to be mercy-killed by Scar. While the main reason he did this is because he was being pressured that without "interesting" results from his experiments, the government would kick him out, Tucker later admits that he "didn't have a reason", and eventually would have gotten around to doing it just to prove he could. It's next to no wonder that Ed massively snaps on Tucker and Al has to keep him from beating him to death right there.
    • If that wasn't bad enough, there's also The Reveal that he did the same thing to his own wife two years earlier. That first talking chimera that got him his certification? The one who Mustang was told had claimed to want to die and refused to be fed until it eventually starved to death? Yeah. And of course, just for bonus Kick The Dog points, he lied to Nina and everyone else, claiming her mother had left them.

• Fullmetal Alchemist (2003):
  • Basque Grand crosses this in the past when he coldly forces Mustang to kill Winry's parents because they were helping Ishbalans, which led to a desperately guilty Mustang almost committing suicide over the incident and having to be stopped.
  • Dante creates and maintains a military dictatorship and has her minions, the homunculi, go around stirring up conflicts and encouraging people to engage in forbidden alchemy and human sacrifice — all for one goal, to create the magic stone that will allow her to keep on living forever. There's how she kidnaps Ed's friend Rose and her baby, brainwashing the already mentally-broken Rose into an Empty Shell that will be her new host.
  • Pride plows right through the Moral Event Horizon at the end of the series when he remorselessly strangles his son Selim to death for bringing his remains (having no idea what they really were) to him during his battle with Roy.
  • Majhal crosses it when he tries to transfer the soul of his lost love into a child's body.
  • Bald threatening to slaughter everybody on a train if his demands aren't met.
• Fullmetal Alchemist: Brotherhood (and manga):
  • It's clear from the beginning that Envy is evil and would kill anyone if it's amusing or he's ordered to, but one of two scenes becomes his Moral Event Horizon crossing. For some, he irreparably crossed the line when he killed Hughes after turning into his wife Gracia to keep him from striking back. And if that didn't do it, there's the scene where he gleefully describes how he started the Ishvalan war by turning into a war-opposing soldier and shooting an innocent child. His absolutely cheerful description of the events that happened after he shot the child, how it ruined the life of the soldier he turned himself into, and how humans are so easy to manipulate revealed him for the monster he really is. What he said got Ed so angry that he punched Envy in the face so hard that Envy's face had to regenerate immediately afterwards.
  • "The Gold-Toothed Doctor" spends most of his screentime crossing the Moral Event Horizon. He's responsible for experimenting on people to make human-based homunculi; except for the one who became Wrath/King Bradley, all of the subjects died or were rendered mindless and used as Elite Mooks. He later slits Riza's throat in an attempt to force Roy Mustang to open the gate.
  • Homunculus/Father crossed his in his backstory when he manipulated Hohenheim, the King of Xerxes, and the King's Alchemists into making Philosopher's Stone bodies for both himself and Hohenheim out of every single soul in the country. Seeing the MO of this guy's Satan-based objective in action is truly horrifying. And then he does this again in Amestris. Fortunately, Hohenheim was able to undo that one.
    • The King of Xerxes crossed it by permitting massacres of his citizens to carve crests of blood into the land so the ceremony can occur.
  • Pride crosses this when he eats his brother Gluttony alive to gain his sensory abilities for a momentary advantage in a fight. Even hardened onlookers who were trying to kill Gluttony themselves at the time were shocked and disgusted, and one of them was Kimblee.
  • Brigadier General Clemin declaring Mrs. Bradley expendable after she's kidnapped by Mustang.
  • Wrath crosses it when he bluntly refuses Ishvalan spiritual leader Loug Lowe's offer to sacrifice his life to end the conflict in Ishval, coldly saying that one life is only equal to one life, and that he plans on exterminating the Ishvalans anyway.