Really? I've never had that expectation. I consider it the same as sitting on a seat on a public transit bus or subway train.
I still think the airline should disclose when and how they're recording me, but an expectation of privacy? Nah.
Most people expect some level of privacy when sitting at their seat. This is not a general/overview cabin camera, this is literally a foot in front of you and pointed directly at your face.
I guess the whole controversy seems very knee-jerk and out of touch with the existing level of monitoring already on board the plane and in the airport.
You might reasonably expect a bouncer or a security guard at a concert to be overlooking a crowd. You wouldn't expect one assigned specifically to you breathing in front of your face.