There will be more terrorist attacks. And at least some of those terrorist attacks will be coordinated via tools like iMessage and WhatsApp. It's not a matter of if, it is a matter of when. This wouldn't be because these specific hypothetical terrorists are smart and know to use encrypted tools: If they were smart they wouldn't touch a smartphone for coordinating such an attack.
Even so, I do not support a back door for law enforcement, for three reasons:
* Engineering practicality: It is a very difficult problem to solve in such a way that does not lead to abuse. Once this infrastructure is in place, it is only a matter of time before it starts being used inappropriately.
* Legal practicality: The makers of these devices do not control what applications can be installed or run on their devices, which would allow actual secure communication. Also, would it cover systems like OpenPGP? What about devices without cellular radios, like laptops? Do they get backdoors, too? If not, why not?
* Practical effect: Even if law enforcement has these capabilities, and even if 100% of terrorist attacks were coordinated using iMessage, there is no guarantee that they would be able to prevent all terrorist attacks. In any case, if such laws are put into effect, the terrorists will find other, more secure, ways to coordinate. Attacks will still happen.
The bottom line is that I have seen no evidence that such capabilities significantly improve our security, and, as a free society, we have a great deal to lose by implementing them.
And when we implement these things and people are still dying, what's the next move? What's the next liberty that we will be called upon to sacrifice at the altar of security? Those who care about the 2nd amendment, take note.
These terrorists want to turn us into the very thing we once feared: a George Orwell novel. Turns out it wasn't the Russians we had to worry about: it's ourselves. With the help of the terrorists, we will all run into the loving embrace of Big Brother's protection—and lose everything we hold dear in the process.