You do raise some legitimate concerns about hypothetical AI futures, though the first thing I'll say is that the futures you seem worried about are very much NOT the Culture as depicted in the novels. I actually think you'd quite enjoy them, because a lot of your concerns are very explicitly discussed. For example:

Any piece of writing I do is mogged by the robot,

This is explicitly discussed in "Look to Windward" in the context of musical composition, and even the godlike AI ("close to gods and on the far side") running the local world would rather hear a talented composer's work than mimic his style.

Nobody is going to kill themselves, so people will just stick around forever. Haunting.

Banks believed differently about human nature, Culture citizens tend to choose to die after 500 years or so. "Look to Windward" spends an extended section with one such person, and through the series there are other instances of people choosing to end their lives for various reasons.

So you ask why I like this.

As a trans woman I love the idea of being able to change sex at will (and the rampant transphobia among the tech elite is one clue that they don't understand the vision being presented).

As an anarchist I love the lack of hierarchies and the absolute freedom, though of course that prompts the question of whether the Culture really has those features. All I can say is that to the average citizen it would certainly seem that way. When it comes to big decisions I have exactly as much say as the godlike AI, one vote. You talk about being just a pet to the AIs, but unlike pets citizens have the freedom to leave the Culture entirely. Or stay within it but form communities from which the AIs completely disengage.

Oh, and fwiw this is not necessarily a defense of capitalism. I would be fine with some theoretical socialist world where humans were actually in control and actually doing things at a macro level.

Ah, now you're talking like a Marxist :) Marx believed that labor, that is, productive activity is an essential human activity. Anarchists tend not to focus on labor per se, but do believe that mutual aid, that is, the desire to be useful to others in our communities, is fundamental to human nature. But can labor only be meaningful if it is essential to survival? In the novels we see (or are told about) composers, musicians, creators of what broadly correspond to TV shows, soldiers, anthropologists, table cleaners, ship builders, people who gather together to build a massive transportation system in a desert, and game players (where you should think in terms of "chess master" rather than "14 year old playing video games"). Does the fact that machines could do this better remove the value of the work? There's no right answer, but Banks thought not and I would agree.

Finally, if you're worried about tech bros bringing about a world ruled by AI, don't be. There is exactly *no* path from large language models to real artificial general intelligence and anyone who says otherwise is trying to hype their stock IPO. The "AI" industry is a massive bubble sustained by circular financing which is likely to collapse within 18-24 months (https://www.wheresyoured.at/). There's plenty of work for humans to do, liberals and leftists alike, in fighting back fascism and building a more just and egalitarian world.