Further, not everything landing at an airport is as large or as robust as a commercial jet aircraft. A light plane could easily be severely damaged by a small UAV. Likely, no - I've been in small planes hit by birds - we've survived but it's not a given.
UAVs have no business anywhere in a controlled airspace unless they are under control of a qualified operator AND other pilots know it's in the air. Now, that doesn't answer the question whether somebody should (or shouldn't) be allowed to play with their Phantom II in the neighborhood park. Those things, with the operator using a modicum of common sense, are pretty safe. The problem is the phrase 'modicum of common sense'. We all know that some random jackass is going to lose control of the thing, turn a poodle into poodle-chops or knock a Vespa into oncoming traffic.
While the cretins in /b/ might think it funny, the rest of the planet might take offense at that sort of behavior. Hence, regulation.
This is why it's hard to have nice things.