Well, they are quite correct.
No, they aren't, for two very obvious reasons.
If standard ISP encryption is backdoored, criminals will simply use their own homebrewed encryption apps that don't have backdoors. Sure, that might be illegal, but you think a terrorist or paedophile will care?
In the meantime, the honest folks who are forced to use backdoored encryption for their banking and shopping will suffer at the hands of fraudsters who've found the backdoors and are abusing them.
Mandatory backdoors do absolutely nothing to stop criminals, they just inconvenience honest people.