Those who would give up essential liberty, to purchase a little temporary safety, deserve neither liberty nor safety.
Benjamin Franklin
And anyway, if they ban or hack into encrypted messages, terrorists will just start using steganography and there are loads of apps
http://www.jjtc.com/Steganography/tools.html. So we sacrifice encryption, allowing the not so good people a back door into our data, whilst doing absolutely nothing to stop terrorists using steganography and other methods to communicate in secret.