On 3, I don't know about pedophiles but terrorists do indeed use consumer apps; they're 'good enough' and the traffic doesn't stand out. Many (most?) cases are broken open because law enforcement turns a human source or manages to place someone undercover.
Of course, those apps are not all that they use. There are definite advantages to things like encrypted digital radio vs IP communications, and concomitant downsides such as standing out like a sore thumb in the RF spectrum or being more vulnerable to zero-days against niche platforms.
The problem with the idea that if all consumer apps played ball with law enforcement (and as always, I would like to point out that it isn't clear which nation's law enforcement agencies are supposed to get access) then suddenly there would be no choice but to roll your own encryption tools is naive. It is born from a type of politician's mindset where communication between people is done via an 'app', and an 'app' means that there is a large company that invariably wants to deal with the US or the EU that can be pressured into building a backdoor. And for 99% of today's messaging apps they are right (which is a nice mess we're in by the way).
But anyone can use OpenPGP (or any other tool) today, and anyone can tomorrow, even if such a project stops completely. The source is out there, and so is the source for hundreds of other related tools. There will also be people with — subjectively, depending on whom and where you ask — non-nefarious reasons to have their communications end-to-end encrypted who will find ways to provide such software in a decentralised manner without the point of failure that laws like EARN-IT target.
Of course, those apps are not all that they use. There are definite advantages to things like encrypted digital radio vs IP communications, and concomitant downsides such as standing out like a sore thumb in the RF spectrum or being more vulnerable to zero-days against niche platforms.