Mass surveillance causes significant problems regardless of whether intelligence works, and so not only does it make sense for the IETF to write that "Pervasive monitoring is an attack" but I believe that it's morally right for us to say that therefore we should demand our governments desist from such attacks.
But that article takes a pretty typical Adam Curtis angle when it comes to facts that dismantle his core thesis - acknowledge them very briefly and then carry on as if they didn't exist. Double Cross is less than a hundred years ago and took place under the circumstance in which actual spies are more valuable - a war. It can and should continue to be held up as an example of how actually sometimes (in a war for example) there are enemy spies and turning or eliminating them can be significant.
In the modern era we fight a lot of actions short of war. The most significant subsequent military action in the UK was the Falklands in 1982. But something like Double Cross would have been pointless. Britain did not go to war against Argentina. Argentina wasn't at with Britain. Both countries disagreed about the status of the Falklands, which the Argentinians had (for local political reasons) decided to just seize by force. Because this wasn't a war per se, our "intelligence" was mostly just a result of being friendly with the (similarly awful but not hostile to us) regime in neighbouring Chile. No James Bond types, just somebody who will turn a blind eye to human rights abuses and focus on immediate military intelligence resources.