This argument always bothers me.
Do you really expect people that are involved with child pornography to go “Oh well, now that it’s forbidden to have private messaging I guess I will just stop looking at children, because the law is the law and I have to follow it.”?
These people know they are breaking the law and I can promise you this. They will find a way to privately exchange their shit while the rest of us now have even less privacy…
Encrypting files that can only be unencrypted by one other person is still a thing. Sure it’s not quite as convenient as it happening automatically in your chat app. However, anyone who thinks weakening e2ee in chat apps actually stops illegal actions occuring needs to think a bit more carefully.