Not being antagonistic.
A 3-5 pound rock or quad copter hitting my glider at 55knts or better (glider speed) can do a lot of damage and even come through the plexiglas and knock out the pilot. A "glancing blow" on a wing would still make a pretty big hole in the leading edge or damage a horizontal and jam the elevator.

I can see another "full scale" glider, seeing a quad copter at a range that I can expect to maneuver and avoid, not so much.

Flying these birds or any RC aircraft at a public airport without airport management approval and a safety observer is against accepted AMA rules.
Flying these birds with FPV without a safety observer and out of "line of sight" of the safety observer is against AMA rules.
In the US, the FAA expects all RC operators to abide by AMA guidelines and accepted practices.

There have already been "accidents" of hobbiest pilots of quad copters losing control and causing personal injury at public events.
This already has the the FAA's attention.

BillT