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In short: while a lot of things in the Declaration are a-OK, many are also utter bullshit. Hence the above post.
The document shows its age, specifically the fact that it was written at the beginning of the Cold War, with all the political maneuvering and negotiations arising from the needs of that time.
Now we know more about how industrial and information age societies work, and there is no need to make compromises and ideological bids against the Soviet Union.
Secondly, those countries that would be positively affected by implementing the declaration as written don't give a damn anyway and no one can make them. There is no reason for western countries to not ignore the dumber parts in a similar way, but the core of the issue is with their political class, a lot of which would prefer to add even worse points to the declaration if they had their way.
Some of the questionable points were specifically meant to mess with the Soviets, with more, or usually less effect, but that's obsolete now.
Also back then there were no failed states in modern understanding, as the colonial powers were still more or less present in the third world when the declaration was written, so it's not really well designed to handle those and issues that arise with them.