In all these threads everyone is coming close to the crux of the issue, but I want to restate it in clearer terms:
There is a sacrosanct line between "public" and "private," "mine" and "yours." That line cannot be crossed by Western governments without a warrant. Cloud computing has deliberately blurred this line over time. This on-device scanning implementation blows right past that line.
Our tools before the computing revolution, and our devices after, become a part of us. Our proprioception extends to include them as part of "self." A personal device -- a tool that should be wholly owned and wholly dependable, like pen and paper -- that betrays its user, is a self that betrays itself.