A civil rights lawsuit is fine. But the problem is that doesn't PREVENT any police behavior.
1. hit the kill switch
2. tell protesters to GTFO
3. they don't comply so start shooting
4. no recordings of what happened are made so it's he said she said
5. innocent people are dead and the only recourse is a lawsuit based on conflicting sworn testimony where officers are generally held to be more reliable than non-officers
Contrast this with the no-kill-switch situation
1. tell protesters to GTFO
2. they don't comply and are filming
3. knowing they are filming, use less lethal means of dispersal
4. nobody is dead and the police are held accountable for the actions they took
The problem here is that in the absence of any hard evidence to the contrary the 6hr window gives the police plenty of time to either find a good reason for why they did what they did or if there's some particularly bad actors around, make up a good reason.
I think the vast majority of police departments wouldn't abuse their power especially considering how very nearly everybody doesn't get shot by the cops on any given day. But the concern here isn't that they'll shut down people's phones when making a traffic stop; people are concerned about the possibility of really bad actors who haven't been caught yet using this as a tool to conceal something really bad.
Being able to take pictures or video but not upload them destroys a lot of the utility of a mobile device.
If you can't take a picture and upload it before you get arrested then whatever was on your phone can go away. But once it's uploaded it gets much, much harder to make it disappear.
I will concede that it's not as bad since the camera still works. But that doesn't make all my worries go away either.
Then don't enable this feature on your phone. The law also requires that the feature be explicitly approved by the user and that it can be disabled by the user at any time.
They have a thing called a stingray which can impersonate a real cell tower for the purpose of gaining information about the phones in range. That would be a very effective way to create a list of phones to temporarily disable.
That would not be very effective for the kind of cover up you were speculating about (disabling phones so they can shoot protestors without it being widely recorded on video).
First, they'd have to set up a Stingray. Then they'd have to get the phone numbers. Then for each number, they have to go to the appropriate company and ask that company to do the kill. Note this only works for smartphones. Feature phones are not required to support a kill switch. There are feature phones that include still and video cameras.
That's going to take a while...and it is going to miss a lot of people in addition to those using feature phones. It will also miss tablets, laptops, and GoPro cameras.
If, improbably, the only people with cameras in the protest are people on smartphones, they still have almost no chance of making the coverup work. To get the kill switch applied without court approval, they have to claim it was an emergency, and then justify retroactively that shutting down phone communication was necessary because of that emergency.
They will not be able to do this, since it is almost impossible to come up with a legitimate emergency situation where using the slow and incomplete kill switch mechanism is better than simply shutting down the cell towers that serve the area. Going for the kill switch instead of shutting down the towers is practically admitting that they were not actually trying to stop communication (which could conceivably be a legitimate response to some kinds of emergency) but rather were trying to stop cameras (which almost never can be a legitimate response to the kind of emergency that can arise at a protest).
1. Setting up a stingray takes very little time if it's already mounted on a truck or a trailer.
2. Phones and towers are constantly looking for one another so that phones are always connected. This is how you are able to talk while driving or moving. You might get all the phones in an area in a few seconds or minutes.
3. You make a good point about the per-phone nature of the thing. How long before law enforcement has a kill-a-phone API though? Facebook has a dedicated website for law enforcement to get info on Facebook users.
4. Your point about missing other devices is also a good one. But again the police can arrest people and prevent the information from getting out.
5. I think your statement about simply shutting down the towers is the best counter-argument. You're right, they can just kill the towers, even without phone company assistance. Send a few officers with bolt cutters and towers will go dark.
6. There are all kinds of after-the-fact justifications for doing something especially if you're in control of the situation. You can claim basically whatever you want. Law enforcement is generally considered more reliable by the courts than regular people; cops say X and protesters say Y and judges are likely to believe the police. This is well documented.