True, cameras can be taken away or smashed after the fact destroying evidence.

With my phone I can stream video to a cloud so that it can't be deleted. The ACLU used to have an app specifically for this but it seems to have been discontinued. https://en.wikipedia.org/wiki/ACLU_Mobile_Justice

If you are ok with the low quality, you could use a radio to transmit fast scan TV to a nearby receiver. Use a repeater if you need to get some real distance.

FPV drones often use this and could be a good source of parts. Or encode the feed and send through a small portable ham radio if you want a challenge. https://irrational.net/2014/03/02/digital-atv/

Sure, just be careful not to fall into the trap of technosolutionism.

I have an Eye-fi SD card which can send photos via wifi. Wouldn't be too hard to make a receiver that send from a raspi or something automatically.

Seems they are discontinued but there are other options that work similar such as "EZ Share"

the world isn't perfect, you do what you can. Just take a small RunCam or something and keep in it your pocket and be discreet when you're using it.