Do you know WhatsApp encrypts your messages? Or do you just believe it because Facebook said so? How would you tell if the app was modified to disable it? Do you decompile and audit every binary sent to you by the Play Store? What abut the binaries your peers were sent? And what if their key directory served you a wrong key?

E2E encryption isn't useless, but I see a whole lot of technical people confused about why it's useful. Namely, it's a legal/political hack. The law says the government can make you hand over data you have. It doesn't say the government can force you to make arbitrary changes to your life or business to enable them to have whatever data they want. Obviously this would be two very different laws with very different impact: specifically, it would be a law enabling law enforcement to compel arbitrary action. Such laws are extremely rare and usually tightly limited.

But if such a law were to be passed, the technical infrastructure becomes useless. FB could just be forced to switch it off.