I disagree. I think the only way to effectively prevent anyone from picking their nose into your letters is protecting the letter by various means, not telling

I disagree. I think the only way to effectively prevent anyone from picking their nose into your letters is protecting the letter by various means, not telling others that they must behave so and really not read what you wrote there. Sure, protecting against powerful TLAs is not easy, but certainly not impossible (always keeping in mind there's no absolutely perfect solutions and everything could eventually wear out). If the otherwise would be the case, many countries won't be so upset with strong crypto. I also believe that laws that try to "protect" privacy are actually worsening the situation, not improving it. That's because they make false beliefs with general population that one's communications are secure, even though in practice they're frequently as secure as an unsealed postcard.