I don't know if I want a 'Kill Switch' available in the phones. I am not normally paranoid, but it seems like something governments would use against their people. I imagine that the Arab Spring a few years ago, which relied heavily on phones to tweet, Facebook, and text each other, might have had different results if their oppressive leaders could convince the phone companies to "kill" the phones of suspected protestors.
I was originally a proponent of a law mandating these kill switches, but the more I thought about it, the more I got concerned about exactly this type of intrusion. Note that the iOS Activation Lock solution is met with "cautious optimism." Why? It does everything that a vendor and a consumer can conceivably do to protect their data and deter theft, short of putting an explosive charge in the thing and detonating the phone while it's in the thief's hands, blowing their limbs off.
The only reasoning I have for the continued skepticism is that it just isn't a government-controlled solution.
Also: the feds are already using the possibility of kill switches as justification for wanting warrantless searches of people's smartphones. So there is absolutely a downside to this.