It should be obvious to HS physics students that really frakin BIG asteroids are a special problem beyond the scope of our 21st century civilization. So is a directed GRB. No action should be taken because none can be. As yet.

HOWEVER, the more likely smaller asteroids hundreds of meters or a couple kilometers in diameter ARE interdictable via nukes and several other proposed means. The convoluted PC anti-nuke rationale has to stop, not to say that there are probably better methods in many cases. Science missions to asteroids, comets, NEOs, whatever to better understand their structures and compositions make sense on so many fronts.