Law enforcement entities that try to prosecute these kinds of crimes doesn't do it by building haystacks of data and then combing through looking for needles because that's a waste of their resources relative to the amount of results obtained. They do it by attacking the endpoints where the abuse or terrorism, or other professional crime has to actually happen. They find a terrorist, or a child abuser or a drug trafficker or they find evidence of their handiwork and then work from there. They see where they get their money, their bombs, their drugs, etc, etc and follow the links as much as they can. When law enforcement is actually trying to target crime they don't go fishing, digitally or in meatspace because that's not an efficient way to obtain results if the goal is to go after some genre of professional/organized crime.
Running a mass operation with no specific target (like speed traps in meat-space or dragnet operations in the digital world) is great for padding stats because you can say "look, we got X pounds of meth off the street" or whatever but it doesn't actually do much to target the professional crime because professional criminals take steps to avoid being caught in lowest common denominator type policing.
Neutering encryption (so that cops can continue to run surveillance dragnets) doesn't do anything to help the cops catch real criminals, that's just a talking point made up by the people who want the government to have the ability to put any arbitrary person under a microscope.
In case anyone doubts the above fact: government agents abuse their surveillance powers to spy on their loved ones.
https://en.wikipedia.org/wiki/LOVEINT
This article was posted here recently, a reminder of how easy it is to become the target of warrantless government surveillance:
https://schmud.de/posts/2020-06-02-mlk.html
There's no reason to believe the government is any better than these criminals. Cryptography must be strong enough to defeat even intelligence agencies as well as ubiquitous so that it'll be hard if not impossible to enforce legal limitations or bans.
93% of the time, the perpetrator knows the child. If you’re seriously worried your children might be victims of abuse, then your first line of defense should be against your own family and friends.
https://www.rainn.org/statistics/perpetrators-sexual-violenc...
The statistics for children are in the paragraph after the first graph.
And this is exactly the case where we want to be able to have digital evidence.
What could possibly go wrong?
Easy: don't let your kid join zoom meetings without your permission/supervision until he/she understands that there are bad people out there.
The reason "think of the kids" works so well to justify blocking E2E all the time is because child abuse happens literally all the time.
When someone solves this problem, and I don't think any of us really believe it to be solvable, we can move on. I don't want the government in my private conversations, but I don't want my kids in someone elses either.
To extend this - we recognise a duty of care to our users and their privacy when we build these systems, but if those users plan and carry out an act of terrorism did we not also have a duty of care to their victims to not aid their killers in planning their murder?
We can't shunt this responsibility forever, the public will not take our side down the road - because we are ignoring the counter-argument even if we wedge our fingers in our ears.