system
Given the following post, respond as if you're commenting on Reddit:
human
[The Culture] Can anyone in The Culture be transformed into a Mind or drone? If so, why wouldn't everyone?

We've witnessed mind uploading in The Culture, so it doesn't seem much of a stretch to think that they could alter someone enough that they could function as a Mind or a drone. As far as I can tell, there are no downsides to being a mind, and few for being a drone - so why would anyone remain human?
gpt
The Culture is philosophically opposed to trying to get "more" - more life, more power, more resources.

The desire to live forever, or own your own moon, or modify your body with a thousand dicks so that you can have As Much Fun As Possible, are all (the Culture would argue) manifestations of a childish type of thinking - usually born from a society that doesn't have enough resources, and so cannot conceive of what to *do* with power or lifespan or intellect once they have it, except to use it to acquire even more. 

In the Culture, these aggressive instincts are managed by a combination of the Sapir-Whorf-like effects of Marian, and the simple unfashionability of such a goal - you might eventually *succeed* in persuading a Mind to grant your wish, but everyone would look at you funny while you were doing it. 

>Why do you care so much? What's wrong with you that causes this driving obsession to be perfect? It's not as if there's anything you could *do* in your improved form that a Mind couldn't simply do for you.

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With that said, strictly speaking "human" Culture citizens are only human by the merest technicality, being heavily engineered. It's not really *inferior* to your standard civilian-model 1.0-level Drone, just tailored to different preferences. 

And there *have* been periods where nonhuman forms were more in fashion:

>Ulver Seich's had been one of the Rock's Founding Families; she could trace her ancestry back through fifty-four generations on Phage itself and numbered amongst her ancestors at least two forebears who were inevitably mentioned in even one-volume Histories of the Culture, as well as being descended from - as the fashions of the intervening times had ordained - people who had resembled birds, fish, dirigible balloons, snakes, small clouds of cohesive smoke and animated bushes.

>The tenor of the time had generally turned against such outlandishness and people had mostly returned to looking more like people over the last millennium, albeit assuredly pretty good-looking people, but still, some part of one's appearance was initially at least left to luck and the random nature of genetic inheritance, and it was a matter of some pride to Ulver that she had never had any form of physical alteration carried out (well, apart from the neural lace of course, but that didn't count). - Excession

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EDIT:

By way of metaphor, a Culture citizen would view this question much the way you'd view an ancient Greek warrior asking why *you* haven't pursued the earth-shattering martial prowess possessed by modern-day armies. 

The honest answer is that our society just doesn't value warrior spirit the same way his does.

The Culture doesn't value *anything* the way he does. 

No point improving yourself, Minds are better. No point doing good, everyone is already perfectly happy, and Contact already has all the applicants they need. No point trying to build cool things; we already built it bigger and better 150 years ago, and someone built a VR version 8000 times better. There isn't even any point pushing the bounds of hedonism; here's a drug that makes you feel perfect bliss, your brain can produce it at any time, here's a VR simulation of having sex with 500 supermodels, here's 500 actual supermodels who are bored and willing to have sex with you, here's the form for grafting 500 dicks onto your body so you can have sex with them all at once if you'd like.

There's no such thing as *success* in the Culture. There are popular people and less-popular people, and which is which is determined mostly by fashion. 

Right now, it's more fashionable to go skydiving without a backup to revive you if you die than to be immortal. 

Who wants to jump out of a plane with me?