Are Drones Dangerous?

Drone hits British Airways plane approaching Heathrow Airport

http://www.bbc.com/news/uk-36067591

http://www.idigitaltimes.com/how-dangerous-are-drones-researchers-aalbord-university-simulate-risk-humans-527360

What hazards are posed by drones?

What can be done about this?

Should there be a licence to fly a drone? 

Look also at this article on Rules for Drones in the U.K.
http://www.bbc.com/news/technology-36072039