One of the advantages of hardware kill switches, shutters on cameras, and the like is social signaling: other people can see them, and can see them being used. If I put my mass-manufactured phone on the table, and you can see the hardware sensors switch is "off", you can be quite sure I'm not recording you.
I think there's a chance for us to normalize this sort of thing, and make it table stakes for a lot of interactions. In a meeting room and there isn't a shutter on the camera? That's breaking the rules and we need to find one. And so on.
Relevant to this discussion, another thought I had is location- and QoS-aware enabling and disabling of the cell radios so I'm using wifi whenever I can, automatically. If I have a good internet connection other than through the cell radio, the cell radio is shut off.
Thank you again for your thoughtful reply and your work.