You quote David Hughes, who appears to question the whole concept of planetary defence. Indeed, for the objects that he describes - the 15- 20km "dinosaur killers" - he is quite right. However, this is not the problem with which the meeting on the 12 November was concerned.
The major threat to our civilisation is posed by asteroids in the 1km size range. At this size an asteroid or comet nucleus will produce global effects on impact, and we can expect such an event, on average, once every 10,000 years. Asteroids or comets capable of causing mass extinction events are much rarer, occurring once every 10 million years or so. Mr Hughes is therefore quite correct in saying that we are in little danger of extinction, but has failed to appreciate the danger from globally threatening objects in the 1km size range, capable of inflicting a 25 per cent casualty rate on our species and reducing civilisation to ruins.