Why is spying on the UN worrisome? Countries spy on each other, because countries lie to each other all the time. It's how countries find out what's really happening as opposed to what's said publicly.
If you spy on the UN, you own it. You have a disproportionate advantage in all negotiations (unless other countries are also effective at spying[1]). You might think that it is fine that the US effectively owns the UN, but its credibility is ruined.
The compromised UN is effectively a body for representing and legitimizing the wishes of the cabal of US allies as if they were the actual consensus of all UN member states.
[1] But it is still not possible for any nation to be more effective at spying than the US, given the UN's location.
The compromised UN is effectively a body for representing and legitimizing the wishes of the cabal of US allies as if they were the actual consensus of all UN member states.
[1] But it is still not possible for any nation to be more effective at spying than the US, given the UN's location.