Re: But does it need to break to create a risk?
"If we're going to include private and military airfields, though - well, I can't even find a map of those. (And I suspect looking too hard would probably get me added to a watchlist.)"
It's not a problem getting sectional maps for aircraft. They always list MOA's (Military Operating Areas), FBO's (Fixed Base Operators) and all manner of airports and helipads. Every pilot needs to know where they can and cannot fly and where they need permission to use the airspace. Airspace is also three dimensional so you have to know what restrictions there are for flying at a given altitude.
The drone license for commercial operation in the US requires passing a test on interpreting the maps. The requirement of putting an identifying number on the drone has one back and forth but I think it's back on again and might be required for both commercial and hobby operation. There is a whole lot of stupid in the US when it comes to drones. Just search "drone fail" on YouTube and be amazed at the people that shouldn't be allow outside of an institution. The best/worst videos usually have the line, "Here, hold my beer". somewhere in them.