Are holes in security infrastructure required to collect metadata? Are keys, data that secures content - considered metadata? They're not content. Since you can't discuss the letters publicly, a claim could be that it is metadata, and compel keeping the request to collect it as such secret - similarly the fight from the silenced party, if there were any fight, could be out of public visibility.

No they aren't. Read the Wikipedia page you linked to.

It's great that you can make claims like this based on zero evidence or even allegations, but there is no basis in fact for it.

What's more the number of 3rd party people that have to be involved in something like this make it virtually impossible that the national security letter structure could keep them all silent, especially since there are numerous foreign nationals in the supply chains.

Go read the huge amount of ACLU coverage of these, or the many articles linked, or the congressional testimony. There are no allegations that this mechanism is being used to do what you say.

Since when has the US government felt limited by its own laws? The naïveté here is incredible.

That doesn’t prove they have done it. But arguing they can’t is crazy.