History MoralEventHorizon / StarTrek

** The last episode has the Female Changeling deal with Cardassian saboteurs by nuking Lakarian City; the resulting death toll is two million. When the Cardassian fleet learns of this, they perform a HeelFaceTurn and begin firing on the Dominion and Breen ships. How does the Female Changeling react to this?
--->'''Female Changeling''': I want the Cardassians exterminated.\\
'''Weyoun''': Which ones?\\
'''Female Changeling''': All of them. The entire population.\\
'''Weyoun''': That may... take some time.\\
'''Female Changeling''': Then I suggest you begin at once.
** The Dominion is revealed to have crossed this line long ago in the Season 4 episode "[[{{Recap/StarTrekDeepSpaceNineS04E24TheQuickening}} The Quickening]]", when they infected an entire planet's population with a slow acting but ultimately lethal bioweapon, purely to discourage other worlds from resisting. This was ''after'' devastating the planet with conventional weapons.

** Admiral Leyton spends most of "[[{{Recap/StarTrekDeepSpaceNineS04E11Homefront}} Homefront]] / [[{{Recap/StarTrekDeepSpaceNineS04E12ParadiseLost}} Paradise Lost]]" as a WellIntentionedExtremist who truly believes he's doing a good thing with his conspiracy to take over Earth and put it under martial law. He even looks sorry when he frames his old protege, Ben Sisko, and has him put in a holding cell. [[spoiler:Until three-quarters through the story, the station captures another conspirator and is bringing him to Earth on the ''Defiant'' to testify. Leyton tells his right-hand-woman that the ship was taken over by Changelings and needs to be destroyed]].
** Liquidator Brunt manipulates Quark into signing a contract that requires him to die to fulfill, or else live in disgrace and destitution. He even torments Quark about defiling his remains after he's dead. Quark even resorts to taking out a hit on himself in an effort to live up to his principles [[spoiler:before, thankfully, he has an epiphany and stands up to Brunt]].
** "[[Recap/StarTrekDeepSpaceNineS02E15Paradise Paradise]]": Alixus crosses it with the reveal that a citizen was locked in a small metal box, without clothes and probably without food or water, for a full day, as punishment for stealing a candle. Any suspicions about the colony and Alixus vanish in an instant, for it's become clear she is an outright villain. And that's before it's revealed that she's the reason that the colonists are stranded on the planet, just to be guinea pigs in her social experiment.
** "[[Recap/StarTrekDeepSpaceNineS04E22ForTheCause For The Cause]]": Even with the past atrocities of the Cardassians, nothing justifies Eddington stealing the replicators. He treats the simple act of the Federation aiding the Cardassians after a war as amoral, as though being born a Cardassian is of itself a crime.

** Gul Dukat was a mad, genocidal, sexually-ravenous dictator to begin with... and then he allied with the Dominion just to get back into a position of power, effectively setting off the chain of events that got his own planet razed to the ground.

** "[[Recap/StarTrekTheNextGenerationS5E19TheFirstDuty The First Duty]]": Part of the reason Nick Locarno was replaced with Tom Paris for ''Series/StarTrekVoyager'' is because the writers, and Creator/RobertDuncanMcNeill, felt Locarno had crossed this. It's not hard to see where they're coming from; Locarno pressured the rest of Nova Squadron into performing a DangerousForbiddenTechnique that was banned by Starfleet Academy because the last squad to try it were all killed, and then after a practice session went pear-shaped and got one of them killed, decided to pressure his surviving squadmates into a DeceasedFallGuyGambit. Although he does take responsibility eventually, it's only because Wesley spilled the beans after Picard confronted him over the cover-up.

** "[[Recap/StarTrekTheNextGenerationS5E19TheFirstDuty The First Duty]]": Part of the reason Nick Locarno was replaced with Tom Paris for ''Series/StarTrekVoyager'', is because the writers, and Creator/RobertDuncanMcNeill, felt Locarno had crossed this. It's not hard to see where they're coming from; Locarno pressured the rest of Nova Squadron into performing a DangerousForbiddenTechnique that was banned by Starfleet Academy because the last squad to try it were all killed, and then after a practice session went pear-shaped and got one of them killed, decided to pressure his surviving squadmates into a DeceasedFallGuyGambit. Although he does take responsibility eventually, it's only because Wesley spilled the beans after Picard confronted him over the cover-up.

** "[[Recap/StarTrekTheNextGenerationS5E19TheFirstDuty The First Duty]]": The reason Creator/RobertDuncanMcNeill refused to reprise his role as Nick Locarno for ''Series/StarTrekVoyager'', instead playing new character Tom Paris, is because he felt Locarno had crossed this. It's not hard to see where [=McNeill=] was coming from; Locarno pressured the rest of Nova Squadron into performing a DangerousForbiddenTechnique that was banned by Starfleet Academy because the last squad to try it were all killed, and then after a practice session went pear-shaped and got one of them killed, decided to pressure his surviving squadmates into a DeceasedFallGuyGambit. Although he does take responsibility eventually, it's only because Wesley spilled the beans after Picard confronted him over the cover-up.

** "[[Recap/StarTrekLowerDecksS4E02IHaveNoBonesYetIMustFlee I Have No Bones Yet I Must Flee ]]": The displayed humans cross it by knowingly unleashing a KillerRabbit onto the station in the hopes that it'll kill Narj and they'll be able to take over the menagerie. In addition to Narj, their actions get the Pyrithian swamp gobblers killed and endanger the ''Cerritos'' away team.

** In the same epsode, the ''Aledo'' crosses it at transwarp when it attacks the station and gets its sister ships to join in.

** "[[Recap/StarTrekDeepSpaceNineS02E15Paradise Paradise]]": Alixus crosses it with the reveal that a citizen was locked in a small metal box, without clothes and probably without food or water, for a full day, as punishment for stealing a candle. Any suspicions about the colony and Alixus vanish in an instant, for it's become clear she is an outright villain.

** "[[Recap/StarTrekDeepSpaceNineS04E24TheQuickening The Quickening]]": If you didn't want Sisko to saddle up in the ''Defiant'' and wipe out every last Founder in the galaxy ''before'' this episode, then you certainly do ''after'' seeing what they've done to the people of this planet.

->''"He can be charming. He can be generous. He can do the right thing. All of that somehow makes his 'evil' actions all the more despicable, because we know that there was the potential in there for him to be a better person. But sometimes the clichés are true: [[NiceToTheWaiter Hitler loved his dog.]] No human being (and by extension, no Cardassian) is one hundred percent pure evil. But there is a 'critical mass', if you will, where the dark deeds attributed to one person become so overwhelming that they swamp all the redeeming characteristics."''

* ''Series/StarTrekVoyager'': The aliens in "[[{{Recap/StarTrekVoyagerS4E7ScientificMethod}} Scientific Method]]" come across as an entire civilization who crossed the MoralEventHorizon long ago and have just kept on going. They routinely do medical experiments on sentient creatures, mutilating, torturing them, and even killing them if they feel it will benefit their medical research to do so. They feel completely justified in their actions and not only do they feel no remorse or regret over their actions, they feel that what they do is noble and beneficial. Genetically deforming, maiming and killing the crew of Voyager is the NightmareFuel evidence of their crimes and ''that'' is only the tip of the iceberg. What is really terrifying is that their flimsy justifications allow them to murder entire societies with impunity and go on torturing and killing as many sentient creatures as they feel is necessary for their "research."

* ''Literature/StarTrekEnterpriseRelaunch'':
** [[spoiler:Section 31 deciding to let Maltuvis take over Sauria in the name of realpolitik.]]
** [[spoiler:Later on, their using the anti-Ware code to annihilate the tech, dooming dozens of civilizations that need the tech just to have civilization.]]

** The biggest person who crosses this line? General Hakeev of the Tal Shiar. What did he do? Oh, nothing major, just ''[[Film/StarTrek2009 be the reason that Romulus and Remus are now asteroid fields]]''. Later moments include kidnapping innocent Romulans and Remans and performing experiments with ''Borg tech'' on them and capturing random people, including your player, and pitting them in Colosseum matches. Oh, and the reason he does this? [[spoiler:Because he's working with the Iconians, a vicious race of aliens that are ready to take back the galaxy. Oh, and they crossed the line, too, by being the ones who gave Hakeev the means to blow up the planets.]]

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[[AC:Live-Action Shows]]

** John Harrison[[spoiler:/Khan]] has several possible MEH's:
** [[spoiler:Manipulating Thomas Harewood into blowing up a Starfleet institution by curing his daughter's condition.]]
** [[spoiler:Attacking a gathering of Starfleet officers, killing Admiral Pike in the process.]]
** [[spoiler:Betraying Kirk, then attempting to murder the ''Enterprise'' crew after his people were returned to him ([[OutGambitted or so he thought]]), at a point where none of the crew posed any threat to him.]]
** [[spoiler:Setting the fatally damaged ''Vengeance'' on a collision course with San Francisco after believing that his crew had been killed.]]
* In ''Film/StarTrekBeyond'', Krall crosses it during his attack on Yorktown Station; not only intent on killing everyone inside, [[spoiler: but to effectively cripple the diplomatic element of the Federation in [[UngratefulBastard for being assigned given command of the Franklin]] [[DisproportionateRetribution and having his faction of Frontier absorbed into Starfleet]]]].

** Quark comes close when he agrees to help his cousin sell weapons after his investments fall through and his debt piles up. Everyone calls him out on it and he begins to fear it himself. He stops just short, betraying his partners after they try to sell weapons to a regent who plans on killing millions

** Kodos the Executioner from "[[Series/StarTrekTheOriginalSeries The Conscience of the King]]" had murdered half the population of a colony world, picking the survivor half with [[SocialDarwinist Social Darwinism]] having convinced himself it was the only way to alleviate a famine

[[AC:Other media]]
* In ''Literature/StarTrekATimeTo'', Prime Minister Kinchawn crosses it rather early, after he uses his illegally-acquired weapons to shoot down 10 Klingon ships in orbit of Tezwa, killing 6,000 warriors. If this didn't represent his crossing the line, his casual willingness to see millions of Tezwans killed in a Klingon counterstrike, including his own family, certainly does. What makes it worse is his apparent self-image as a WellIntentionedExtremist, when he's really DrunkWithPower. He sees his own children's death as merely a means to acquire more sympathy and thus more support and power, and seems to truly believe this is somehow reasonable.