> That genie's out of the bottle [...] public spaces become obscenely public

A bit "meta" here, but this was never about surrendering to advancing capability, humans have been capable of eavesdropping ever since eaves were invented, people could bring hidden microphones and cameras in "private" spaces for decades, etc.

The "reasonable expectation" doesn't come from our fears of the worst, or else it would be meaninglessly permissive. Rather, it's an attempt to judge individual situations based on some kind of collective agreement about normality. Just because we can't preemptively block something doesn't mean it cannot be a crime.

In other words, we (should) have a lot more power to decide what they become than that. Supposing--and I'm not endorsing this--anyone caught recording in public typically gets their stuff smashed by an angry mob, then the "reasonable expectation" is that you're not being recorded.