Moreover, legal protections exist even where technological protections do not; just because the police have the ability to intercept text messages doesn't mean

Moreover, legal protections exist even where technological protections do not; just because the police have the ability to intercept text messages doesn't mean they have the right to do so without a warrant (and somewhat similarly for carriers). Once you voluntarily give the police — or carriers — permission to read your text messages, all bets are off.