All this is going to do is invade the privacy of regular people, and force 'terrorists' to go off-the-grid which will make them even harder to track. The IRA were pretty good at terrorising without any kind of electronic communications - encrypted or not.
ISIS have already built their own chat application, allegedly, and distribute the APK privately. If the government ban e2e crypto in apps like WhatsApp/Signal/Telegram, expect to see more such apps from groups who politicians can't exactly summon into their offices for a chat.
I'm completely against banning encryption, and also against the argument I'm about to use, but the devil's advocate to your comment is to claim that if the only people using encryption are the "bad guys", detecting encrypted data on the networks is enough to spot a "bad guy", even if you can't read their data.
Sure, that is a potential issue with the argument. But the broader argument is that you can't make crypto go away by wishing. You can't unpublish bcrypt, libsodium, OTR, Signal Protocol, and you certainly can't unpublish the maths they are based on.
All you are really doing is making it inconvenient for normal, law-abiding folk to use strong crypto. A suitably motivated attacker (think ISIS, al-Qaeda etc.) could adapt to a world without crypto using some kind of steganographic approach (three poop emojis and a Miley Cyrus gif = blow the building up!). Every approach you take could be manipulated by the bad guys to their own advantage.
She summoned some big tech firms yesterday to tell them how unacceptable it is that the police can't read encrypted messages.