"We have to face the facts, the technology exists. It can't be uninvented. Once it gets out there, it will be abused. None of us can prevent that from happening. But we can choose, where we want to be and on what side when the end finally does arrive. Do you want to be the destroyed? Or the destroyers?"
Kanako from Star Driver uses this as her justification for working with Crux and fighting Takuto.
The warring sides of Gundam SEED use this trope as justification for their deeds; both are led by extremists who aim for nothing less than the complete annihilation of the other side down to the last man, woman and child. Therefore, backing down and depending on Mutually Assured Destruction is equivalent to surrender. Things escalate when both sides aquire N-Jammer Canceller technology and a battle ensues where the Federation launches dozens of nukes at ZAFT's civilian population while ZAFT have a nuclear-powered Wave Motion Gun pointed at Earth; had the protagonists failed to destroy these WMDs, the result would've been a Mutual Kill. Fortunately, the extremists are killed during the battle, after which both sides have a Heel Realization and finally begin negotiations.
In the X-Men comics, this is one of Magneto's main rationales in his war on humanity, and one of the main sticking points in his philosophical differences with the more idealistic Professor Xavier.
When John Constantine was hired by a corrupt adviser to the Royal Family to discreetly resolve some demon business, his anarchist friend tried to warn him that they'll betray him as soon as his work is done. John is not unaware of the possibility, and reassures his friend that he will follow his usual strategy: "Screw them before they screw me."
The explanation for the construction and deployment of DESTINI in The Core: "Someone was going to build it, so we built it first."
Said word for word in Van Helsing, with Dracula starting and Igor finishing the quote. However, they were talking about generally being horrible to people rather than a particular plan or pre-emptive strike.
According to The Men Who Stare at Goats, (which claims that this entry should be under the Real Life section,) both sides of the Cold War ended up doing psychic research mainly because of this trope. Even though not many people on either side actually believed there was anything in it, they couldn't let the other side lead the field just in case it turned out to be real. Explained by ColonelQuaritch at about 0:41 in this video
In the Bad Future the protagonist of Paycheck is trying to prevent, a machine capable of seeing into the future predicts a nuclear war. So the US decides to strike first, starting said war.
An episode of Bonanza had a family of squatters led by a matriarch who claimed no one would give them a fair deal, saying there were two laws, one to protect everyone else and their law which was essentially "An Eye For An Eye." Their conflict with the Cartwrights starts when one of the boys kills one of her sons in self defense after he tried to shoot him in the back, twice, when the Cartwright tried to stop him from setting a clearing fire that would have burned an entire populated valley. Despite their stance of avenging slights the family acts in a way that actually causes confrontations, like squatting on other's land and breaking out rifles every time they meet someone. The matriarch's attitude has caused her sons to act violently when opposed and made it a Self-Fulfilling Prophecy, though most of her children don't agree with her position. In the end, her surviving children refuse to go to war with the Cartwrights and she decides to make peace with the family, ending the feud on a positive note as she accepts Ben's offer to help her family settle in a new home.
In episode 7 of Survivor: Blood vs. Water, Tina reveals to Monica that Kat wants Monica to be voted out, which would clearly break the Galang women's alliance. Monica has a grim realization:
In Larry Niven's Known Space stories, the ARM ("Amalgamated Regional Militia," the police force of the United Nations) exists primarily to stop this sort of thing from happening.
Subverted in the HIVE Series. The big Council 'O Evil's policy is "Do unto others." Yeah, that's the entire motto.
Occurs in the Robert A. Heinlein short story "Solution Unsatisfactory". One of the U.S. characters considers having everyone who knows about the secret of the radioactive dust shot, but decides that the enemies of the U.S. would eventually discover it and use it against the U.S. anyway. The U.S. goes ahead with creating and using the dust itself.
This trope is the very basis of Enderís Game by Orson Scott Card. Instead of preparing to another "bugs'" invasion, mankind chooses to attack first this time.
In Alexander Zorich's Tomorrow War, this trope is a bitter discovery for heroes. They believed they were defending Earth against an unprovoked Concordian invasion, but it turns out the Earth prepared invasion as well, and Concordians only managed to fire first, 'cause they were better prepared.
This line of thinking underpinned much of the nuclear proliferation in the Cold War, and certain generals like MacArthur talked publicly about preemptive nuclear strikes against the Communists. Thankfully, cooler heads prevailed on that one.
It was Hitler's favourite excuse for invading countries, Russia in particular. There's even a Conspiracy Theory that Stalin wouldn't have tolerated the Nazis in his backyard for too long and was ready to strike them first. Very unlikely, though, given how unprepared Red Army actually was at the early stages of war.
Its not just a conspiracy theory, as reputable academics have given that serious thought. The Soviet Union's industrial capacity was at least half again as much as that of Germany and her allies combined; Germany attacked because Hitler thought it was then-or-never. The typical conclusion is that no, Stalin wasn't planning to invade in 1941-2, but Stalin would almost certainly have done it when he felt the Red Army was ready. Which it certainly wasn't, in 1941.
Hitler 'thought' it was then-or-never. When given accurate reports of the Soviet Union's industrial capacitynote They produced at least twice as much everything as Germany did at every stage of the war, with the exception of trucks and aircraft; the USSR 'only' produced 15% more aircraft of all types than Germany did, he flat-out refused to believe them. German defeat was always inevitable because of the Soviets' ability to mobilise their people and produce war materiel; the Red Army's abysmal performance in the summer of '41note Largely the result of Stalin's failure to plan for such an invasion, and his insistence on keeping the Red Army camped 'right across' the border from Germany (like a total strategy-noob) only made the war 'look' like a close-run thing. In reality, capturing Moscow 'and' Leningrad 'and' Stalingradnote A total impossibility, but bear with us before October of '41, it still wouldn't have been enough to win. Taking territory is very different from holding onto it, and Soviet industrial capacity would still have remained largely undiminished. The only question on the Eastern Front was how long it would take, and how many people would die, before Germany fell. The answers would appear to be 'four years' and '28 million', respectively.
This is a popular theory for why people allowed the commons in medieval England to be overgrazed. "If I cut back and give the fields time to recover then someone else will just come along and overgraze the field anyways. They'll have better fed cattle and I'll be cut off from a free resource." And that was a real tragedy.
This is the sort of reasoning that Thomas Hobbes feared would dominate people's actions in the absence of an all-powerful ruler whom none could overpower (making it downright suicidal to shoot first, last, or ever). He thought that even genuinely good-natured people would be motivated by worries that their neighbors might not be equally peaceable, leading them to kill lest they be killed (though it should be noted that Hobbes believed most humans didn't need this excuse).