In reply to Pyreneenemec:
Ah I hope I wasn't misunderstood... my thoughts were more at the loss of privacy and whether our world will be better or worse when there are no walls. The blacksheep stuff from London, as an example, has the aircraft flying round the houses of parliament. It's a security nightmare. As a weapon delivery system or a weapon in itself they will become a problem.
In terms of the safety of the them well a risk is really a probability multiplied by a consequence.
So for a large airliner the probability is vanishingly small, but the consequence is huge so we take lots of mitigating steps to reduce the risk to acceptable levels.
I'd say the chances of a drone crash is quite high, but the consequence is harder to quantify. At 0.5 kilos falling out the sky onto your foot, sore but meh. Going through the window and hitting the driver of a London bus in the head... nasty.