Think of Midway Battle. Think of Enigma.
You can say, hey look that proves US/UK govt can spy on you. Never mind Japan/German nations were at war with US. But I digress.
But if those didn't happen, you and I all have a high chance of being a second class citizen (or just a person and not a full citizen) in some totalitarian state in modern date, either being forced to use German or Japanese language. And that is if you are lucky. Many in modern time have a high chance of not being born if German/Japan won WW2. And key battles in WW2 were won by Allies due to breaches in communication network of Japan/German.
Yes, US/UK or any western govt spying on citizens is distasteful. But the communist Chinese govt spying on you and using that information will be far worse than that.