I think that the outrage doesn't come from supervised learning, rather that it's contracted out to a third party and seems to be done in a irresponsible way. I think that the fact that most of the public that uses these devices would be surprised by the fact that their voice is being recorded and transcribed is the irresponsible part. Of course a ML engineer is going to want to go the route of human labeling the audio data, and these folks seem to have won. You can blame the public for being uniformed, but it's new technology, and most aren't going to have read up on the methods used, even if it's no secret. Many have suggested other opt-in methods, which would also provide (arguably less real world) data. I think that many would prefer to trade a less accurate service for not having strangers listen to their conversations.