I'm not seeing anything that constitutes an argument here.
Merely that you state a fairly well known text happens to agree with you.
That's all well and good but of no actual relevance.
You evidently dislike the Culture, at least as portrayed in this thread. That's fine. I think I could absolutely despise what I've heard of the Culture as it touches on purely personal and in some cases theological assumptions that we need not dwell on here. I consider it as an idea a rather foolish and possibly immature fantasy that could never come to pass. However I've heard in previous discussions of indications that at the meta level the series is aware of it and perhaps even acknowledging the impossiblity as a fair point... but what if it was possible?
Which intellectually can make for an interesting exercise in exploration of the ramifications.
However suggesting 40k has some kind of moral superiority that we should prefer it over the Culture... is a monstrous confusing of priorities. Oh sure humans are in charge, and failing badly. Any kind of value in being a Man's Man Universe is dust between failing to maintain a functioning society who for 40,000 years of history and 10,000 years of rule often fails to provide the standards of living we First Worlders expect.
And certainly to mention how the entire universe outside the Imperium wants to rape humanity to death, eats its flesh, and sew its skin onto its clothes that if the Imperium is very, very lucky will happen in that order.
Something as esoteric as valuing human achievement means nothing in the face of starving underhivers and Guardsmen fed down the throats of hell in an failing attempt to drown hell in blood.
I'd live in the Culture. I might end up being the relative equivalent of an ascetic living in a jar in a public square... but it would be the "relative equivalent" with emphasis on relative because the point would be reforming the Culture. To have my cake and eat it too.
I would not live in the Imperium.