>Banning a single service such as WhatsApp is not a solution to this problem.

Generalizing this argument a bit, banning encryption is also not a solution to this problem. The cat is, as they say, out of the bag, and unless we're going to burn every cryptography book and remove every website documenting cryptographic methods or hosting cryptography code, there's no putting it back [1].

1: Presuming the development of effective post quantum cryptography cannot be prevented and distributed, which considering the current state of PQC seems unlikely.