Chopjock,
I think Crab's point was why introduce a completely unregulated hazard into the sky when we do a reasonable enough job of crashing the regulated ones into each other already?
They don't have to be here to stay and while I agree that many professionals have them and use them perfectly safely, it's the ones like the goon in Istanbul last year which worry me. it only takes one.
Every time we fly with these around it reminds me of an old military phrase about enemy action: I have to be lucky every time, they only have to be lucky once. Sums up my sentiments of the risks of drones perfectly.