Just because someone can abuse a thing doesn't make the thing bad, it makes the person who commits the abuse bad. We don't ban cars to fight drunk driving and we shouldn't eliminate the spirit of the 4th Amendment to go after child pornographers, terrorists, money launderers and drug dealers. Even with E2E encrypted communications the fact that user A is communicating with user B, when, and for how long is knowable, and that metadata alone can be sufficient to get the warrants necessary to effect legal, invasive searches without disturbing the rights of everyone else.