Maybe you don't understand the historical context here. During WW2 the various allied forces were able to gain an advantage by breaking NAZI codes and the codes used by the Japanese Imperial forces. By having advanced knowledge of enemy movements, allied forces were able to defeat enemies with superior forces. Specifically, they were able to destroy the Japanese surface fleet, and the German u-boat fleet.
Intelligence acts as a force multiplier. And after the war, governments took notice of the important role it played. It's fun to talk about hostile organizations like they don't exist or they threat they pose is overstated. But the reality is they do exist, and signals intelligence is an important part of any strategy to combat them. It's naive to suggest that the US government could be stable in the long term without it.
That said, it would also be foolish to operate this program without oversight and transparency. As I said, an obvious potential for abuse exists and has been overlooked.