Why are cell phone kill switches a bad idea?  Let’s consider a couple perspectives.

Good People with Good Intentions

Someone believes that their cell phone has been stolen, so they call the cell phone company to report that their phone has been stolen.  The cell phone company triggers the kill switch.   5 minutes later, the person discovers that they had simply misplaced their phone.   Now they have a useless paperweight.

Bad People with Bad Intentions

A cell phone is stolen and the robber immediately takes out the battery.  With no way to communicate with the cell networks, the phone cannot be remotely disabled.   The bad guy sells the phone to someone who reconditions stolen phones.  Makes a few quick bucks.  The person who reconditions phones brings the phone into room specially designed to not have any wireless coverage (faraday cage).   He then proceeds to reprogram the phone to change the phone’s electronic serial number.   When the phone returns on a cellular network, it can no longer be disabled.

Conclusion

Don’t be stupid.  Don’t put kill switches in cell phones.