I haven't said anything about trusting them. I am simply correcting statements about what the US has supposedly "admitted".
It's one thing to say "I think the US did XYZ".
It's quite another to say "It is an objective truth that the US did XYZ, in fact they even admitted it".
Transposed to the Guardian, if they want to write "we think the US did XYZ", they should clearly frame it as an opinion piece. Instead they are writing "it is an objective truth that the US did XYZ" - which is false. That is journalistic malpractice.
It would be journalistic malpractice to avoid reporting on anything that the government does that the government isn't willing to admit publically to doing. It's possible to ascertain facts, even of the actions of the US government, to a level of certainty sufficient to report them as facts, even when the government disputes the facts.