What altitude was the helicopter my ****! It was fire-fighting!
This is precisely the reason that those who operate legally at low level are so worried about the damn things. They can pop up anywhere and as msjh said when a bona-fide low level aircraft appears there is little time to react. Helicopters and light aircraft operate into and out of remote sites, fly legally below 200ft on some exemptions (power lines for instance, the regular 200ft (!!??? Hmm...) Chinook low-level route by my house) and way below 500 on many others - and don't need an exemption to ground level on open countryside anyway - so drones are a potential threat.
Drone operators and legislators blindly imagining that a height separation solves the problem are severely deluding themselves, as shown by the extraordinarily smug question asked by ATC watcher. Helicopters and light aircraft operate perfectly legally in the airspace below 500ft and it is neither their responsibility nor within their capability to avoid drones. The only one who can do that is the drone operator - and there seems precious little evidence that even the drone guidelines, lax as they are, are even known by many operators (many/most of whom are amateurs of course) let alone adhered to. Go look on youtube to see some of the idiotic things people are proudly boasting of doing with them!
If drones were hard-wired to no more than 100 or 150 ft I'd have thought they'd achieve most of what they need to do and remain pretty safe. 400ft seems vastly excessive to me in view of legitimate pre-existig aviation requirements.
I fear it is only a matter of time before this is backed up by a body count.