[csandreasen]

If you're going to use the envelope analogy, also consider that we don't put our mail in envelopes to prevent the police from intercepting it; we put them in envelopes to prevent access by all of the people handling the mail between the sender and intended recipient. A cop with a warrant can rightly get access to a person's mail in transit. The envelope also isn't particularly difficult to get around - we don't secure our mail through technical measures but instead by putting stiff legal penalties on tampering with it.