Epistemic status: Whimsical
Major spoilers for Madoka Magica, a show where spoilers matter!
Kyubey Shuts Up And Multiplies
Meet Kyubey. Kyubey is a Longtermist.

In the Madokaverse, changes in human emotion are, somehow, net-positive in the creation of energy from out of nothing. The Incubators (of which Kyubey is one, pictured above) are an alien species who've discovered a way to farm human emotions for energy.
Most of the Incubators don't feel emotion, and the few that do are considered to be mentally ill. But humans are constantly leaking our juicy, negentropy-positive feelings all over the place. With human angst as a power source, it's possible to prevent the heat death of the universe!

Do the math, people. The suffering of a few teenage girls is nothing compared to pushing back the heat death of the universe.[1]
And this isn't just some Omelas situation where the girls get nothing out of it. They get wishes! Who could object to a cause this noble?

Homura has Something to Protect
If you want to see Homura kicking ass, you could watch up to 2:22 before reading on.
There's something subtle here—something to notice confusion about, even—where is she getting all these guns from?
Remember: Homura's power is time manipulation. As one commenter puts it:
This is hauntingly sobering when you consider that Homura's magical ability has nothing to do with guns, only with time manipulation. That means all those tens of thousands, hundreds of thousands of pounds of explosive material and weapons arms weren't just made from nothing like Mami's guns were- they were individually tracked down and gathered, one after the other, by one little girl.

How many hundreds of repetitions did it take to find them all, every time making a new doomed timeline? How many thousands of hours did she spend looking for where to get them from, and how many failed attempts finding the most effective way to arrange them?

Rationalists have a name for this kind of determination: Having something to protect.
Magical Girls are mesa-optimizers
When Kyubey creates a magical girl, he offers them an atomic contract: they gain a sparkly transformation and fight witches for the rest of their life, and in exchange, they're granted a wish.
There's a minor risk here: Kyubey can't actually stop this process: the wish will be granted whether he likes it or not.
(I sure hope the mesa-objective pursued by human girls is the same as the outer objective (negentropy) pursued by Kyubey. There are no possible ways this could go wrong)

The Incubators were reckless. I'm glad humans would never apply large amounts of optimization power without guarantees for how it's aimed.
In Conclusion
Hopefully you've already seen the anime (otherwise, sorry for all the spoilers you just read!) but if you haven't, go watch it now. It's great, and incidentally chock-full of fables like these. (For a bonus fable on Kyoko and the complexity of wishes see Ep7, 8:05 - 12:14.)
If you have already seen the anime and want to read something with similar themes, I would recommend Qualia The Purple.
- ^
Though it isn't spelled out in the show, humans appear to be the only species that has feelings, so depending on whether you're a positive or negative utilitarian, a universe full of emotionless beings may or may not be a compelling vision for you.
Where did you hear that TTS inspired dath ilan's Governance?