If cell service can already be at the tower level, being able to kill individual phones seems like it would be very impractical in a protest situation. This seems less prone to abuse than a mass shutdown.
The remote kill switch disconnects people from their ability to document what's happening. This frees the state from a sousveillent presence because it robs people of the ability to record what's happening at all. Remotely shutting down devices isn't about preventing people from tweeting - it's about preventing people from being able to create durable records of what happens.