Principles are principles, but they are interpreted in context. It's not about "fleeting public zeitgeist" but about recognizing that American principles have always been about balancing security with liberty. A lot of people would have us read the word "reasonable" out of the 4th amendment, but it's there and it is what implements that balancing. The question is how to find that balance in a world where China can attack important economic assets digitally instead of having to cross an ocean physically.

I should note that I'm not arguing that the government should read text messages. I tend to think that if you're sending something in clear text so some flunkie at AT&T can read it, its no problem if the government can too. My point is that you can't just ignore the real security concerns. The U.S. has never been about liberty at the cost of security.