The US has laws against snooping on the mail - so before encryption, it was illegal for the government to even try to snoop (search and seizure). The only reason this is even an issue now is that digital information is not being legally treated in the same way as physical information. If we had laws to prevent the government from ever opening your email, that would be a solution worse than encryption (laws are easier to break than elliptic curves), but it would achieve some of the same goals. However, you will never see the advocates of cleartext laws propose that trade - they don't want the same rules as we had in the 1800s, they want looser rules!