> Why are some of these people so obsessed with reading everyone's chats?

Having worked with some of the people in law enforcement heavily pushing this, it generally does come from child safety concerns and the overwhelming amount of CSAM sent via encrypted means.

Personally, I don't believe that it will ever be restricted to serious crimes and the potential for abuse is infinite, so I don't believe it is justifiable, but child sexual abuse is a real and enormous problem that causes untold harm and suffering, so we have to find a balance.