Dr. Schlock from Sluggy Freelance lives and breathes this trope, always betraying someone or another in order to keep a different someone or another from killing him. Reaches its peak in this strip.
Said verbatim by Anakin in this episode of Darths & Droids, after deliberately destroying Sebulba's pod (and possibly Sebulba) to win the pod race.
Krunch's comment to Cale on this page: "You did what you had to do."
While the most poignant example in the comic, not the first. Played seriously and then for laughs on this page.
Later Pella uses it after she kills innocent gnomes to force the rest to evacuate from their fortress. This makes Cale unhappy because at that point she was the only member of his party he was sure would not use that excuse.
In Harkovast, Shogun views killing wounded, surrendering opponents as perfectly reasonable, and angrily defends this concept when questioned by the other characters.
Maxim 20 from Schlock Mercenary: If you're not willing to shell your own position, you're not willing to win.
In Homestuck, Vriska Serket justifies mind-controlling an army of ghosts and sending them all to the post-death slaughter because the threat of Lord English is far bigger in the grand scheme of things than her actions. Of course, her own ego might also be a factor in this. Recently, Aranea Serket decides to steal John's ring and come back to life in order to stop English before he could ever become a threat in the first place, which involves her lying, stealing and potentially dooming the timeline and herself if her plan doesn't work; all of which she justifies this way as well. While it's never quite explicitly stated, Kanaya seems to generally operate on this principle too. That's why she can cut off Tavros's paralyzed legs so Equius can replace them with robotic prosthetics without batting an eye, and why she's more than willing to kill Gamzee after he goes mad (and actually does kill Eridan when he turns traitor) to keep the rest of the team safe.
In Girl Genius, this is Baron Wulfenbach's justification for conquering Europe. The only way to stop the Forever War was to win it himself. And it worked. During the comic itself, he continues in that same mindset, but having only partial information leads him to confrontation with the protagonists while the true villains escape his grasp.
Billy Thatcher in morphE pulls this card on Asia when he cheats on their magic trial to win a phone call to his loved ones outside of captivity. The only reason cheating is even a concern is because of Asia's extreme honesty and good morality. Billy is intent on not allowing her naive belief system ruin their better shots for freedom.
Lord Shojo had some choice words to say when his Obfuscating Stupidity ruse was found out by his underlings, including his nephew Hinjo (who takes it especially hard).
Hinjo: The ends justify the means, is that it? Shojo: Frankly, yes. Hinjo: You have brought disgrace to our name, Uncle. I am glad Mother did not live to see this day. Shojo: Oh grow up Hinjo! My sister was the daughter of a great leader, she would have understood all too well that I don't have the luxury of putting Soon Kim's obsolete morality ahead of the safety of this city. It's all well and good for you paladins to stick to your convictions, but if I make a mistake, half a million citizens pay for it.
Defied by the fiends offering Vaarsuvius a Deal with the Devil. They tell V about an alternative to their offer, specifically in response to V claiming this, to ensure that Vaarsuvius knows they truly accepted the deal out of pure Pride.
O-Chul says this about destroying Soon's Gate rather than letting it fall into Xykon's hands, something he took responsibility for even though he didn't do it himself. Unfortunately, the person he's talking with would rather let Xykon have the last gate than let the remaining gate be destroyed and release the Snarl.
While not on the same level as wars and battles, in Gunnerkrigg Court Annie has succeeded in a dangerous plan that involved a bunch of her friends but nearly got them killed. They all agree with her that it was the right thing to do. One of them says this for her:
Red: Well you did what you had to do, I guess.
Unordinary: John says this word for word when Arlo confronts him at the infirmary for having sent Isen there. Arlo verbally subverts it: if John's only goal had really been finding Sera, he wouldn't have been so violent, as there was no need for it. John admits it quite quickly that he went out of his way to make Isen suffer out of a desire for revenge. That's something of a running theme with John: he claims to be out to do what is necessary, but it's undeniable that there (also) are many personal motivations behind his actions.
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