ac and Sham:
The problem is it will NEVER just stop there. You can call it paranoia all you want, but if you start allowing the government to monitor your personal correspondence to "protect against terrorism," then it's not that much of a leap before the secret police comes knocking on your door for any critical opinion you may have about the government. It's little abuses to freedom like that "for the greater good" that are EXACTLY how police states start.
I don't care WHAT kind of world this is now. Safety and security are NOT legitimate reasons for these breaches of personal privacy that are SUPPOSED to be protected by the Constitution and Bill of Rights, and frankly I find that sort of "ZOMG WE MUST STOP THE TERRORISTS!" alarmism FAR more troubling that the "tin hats." These protections were established PRECISELY to prevent the sort of idealogical persecution that was happening in parts of Europe during the 17th, 18th and 19th centuries.
I guarantee you that if people give up one or two little freedoms in the illusion of safety without so much as a word of protest, then a whole lot of BIG freedoms will eventually follow.