The risks are very high in shooting at a tiny, fast moving object flying close to a huge amount of aircraft and jet fuel!
I think it is great that finally, after years of pilots telling the CAA and government that they need to sort out the fast growing drone problem, they are finally doung something. As for a drone closing an airport, many things close a runway, including aircraft emergencies, inbound emergencies, animals on the runway, people straying onto the protected area. People are so used to how safe aviation has got, they forget the potential dire situations aircraft could end up in. Pilots will always err on the side of safety. It is always better to be on the ground wishing you were in the air, than in the air wishing you were on the ground!