References please

Agree, but why? It's an interesting theoretical question when you think about it. Is it because people who have the money and means have a skewed concept of the world making them incapable of constructing utopias/well functioning "synthetic societies", or is it more fundamentally impossible? And in the latter case, why then should we even try to improve society?

Because every organically developing system has a great advantage that these projects lack: time. Cities evolve by gradual corrections/adjustments, you cannot anticipate every issue upfront.

Ideas needs to adapt when meeting reality.

I don't even know if it's true, but if it is I'd guess the Typical Mind fallacy: most of us have blind spots where we don't think about how "good" people in a hurry would react, let alone the power-hungry actively trying to break it for their own gain.

I actually can’t think of any good examples. Brasilia? Chandigarh? Irvine? All seem fine relative to their neighborhood.

In practice or in fictional books? If in practice I’m sure you can share a handful of examples.

Sealand

Fordlandia:

https://en.wikipedia.org/wiki/Fordl%C3%A2ndia

And for a really dark example:

https://en.wikipedia.org/wiki/Colonia_Dignidad

Also Disney's failed attempt:

https://en.wikipedia.org/wiki/EPCOT_(concept)

Finally an example that actually worked:

https://en.wikipedia.org/wiki/Siemensstadt

...the project reminds me much more of the Chinese 'fake European cities' though:

https://www.telegraph.co.uk/books/non-fiction/duplitecture-d...

Some examples: https://en.wikipedia.org/wiki/Freetown_Christiania (ongoing experiment, I guess), https://en.wikipedia.org/wiki/Fordl%C3%A2ndia, Soviet Union