At NASA, I was told that the reason for the focus on threat of asteriod impact, which they admitted was laughably unlikely, was because it could bring in more money. (illconsidered.blogspot.ru)
Since we can not examine the real world in the absence of forcings (there is always solar variability, volcanic eruptions, orbital forcing and random events like asteriod impacts), it is a valid working hypothesis to assume the models are reasonable. (realclimate.org)