We always assumed the letter carrier could read our postcards and could notice the return addresses on envelopes. Not that I really suspected them of doing it. They were probably too busy to care. But I never assumed that these things were private. Some items came in plain brown packages so no one would know who was receiving them. Oddly enough, I can’t remember what those items were, but I know I read ads for them.
People talk as if there were a constitutional right to privacy. Aside from it not actually being in the constitution, I don’t think people really thought about it in the terms we do now. Before the invention of railroads, the vast majority of people lived in rural areas where they were well known. Strangers were watched and distrusted. Anonymity existed in cities and large towns, but most people lived in the country. In 1790 in the USA, farmers and other agricultural workers were 90% of the labor force. Local support for farmers probably added a couple of percent. Farming communities needed blacksmiths and harness makers.
People living on farms or in the small supporting communities rarely traveled long distances. Travel was very expensive in both time and money. The result of this was that people didn’t have privacy as to where they were. The chances were high that someone who knew them noticed them.
Anonymity is a modern invention. As long as human hands held the envelope, someone would know who was writing whom. As for telephone information being private by constitutional rule, the telephone was invented long after the constitution was written, and until the mid twentieth century, most phone calls were handled by human operators.
Making the assumption that NSA is telling the truth and they aren’t listening to our phone calls or reading our emails, we have no complaint. It has only been a short time in history when those things were genuinely private. If terrorist plots are foiled by this lack of privacy, it is a small price to pay.