[Filligree]

They did. It isn't explicitly stated, to the best of my knowledge, but the Minds are smart enough that they could easily have done that—and were shown to engineer other parts of the society, such as their deathism.

Humanity has very limited purpose in the Culture. On the surface, it looks nice, but they're effectively pets. Their willingness to ascend was cut off right along with their willingness to live.

All of which is done by social engineering. If you want to go the intelligence-enhancement route, they'll help. They just make sure that very few people do.

[david-given]

That's true, but it's also rather deceptive. Humans are the fundamental core of the Culture; its basic purpose is to look after human-scale people, and this shapes everything it does --- the Culture's a bit suspicious of ascension because they feel it's an abandonment of their responsibilities. Humans are, in effect, the Minds' religion.

And dying is just one of several end-of-life events you can pick, if you want to (including opting out entirely). Naturally it's the one we tend to focus on, because it's the only one we currently have, but the Culture's got lots.

[JabavuAdams]

Right, this is where things break down. It's fictional universe, after all.

What are the negative effects of having more Minds? Resource depletion?

If your cat suddenly tells you that what it wants more than anything is to learn General Relativity, then either you're having a psychotic episode, or you have to question how benevolent and ethical your coddling is for your fuzzy wuzzy slave animal.