I agree with Joga - there's far far more pressing things that money could be spent on, especially in this day and age. Perhaps if we were in the middle of an economic boom and had so much money no-one knew what to do with it then yes, but IMO it doesn't seem like a wise use of taxpayers money at present.
To anyone who disagrees, can you quote a hard number at me which is the probability of such an asteroid (i.e. one that would cause mass loss of life) hitting a densely populated area? Then can you compare it against all the other ACTUAL killers around at the moment such as those that require medical treatment and research? Frankly I really can't see the logic of where you're coming from here.
Yes, an asteroid might wipe us all out tomorrow. But on the other hand, you might contract a terminal illness tomorrow, you might get run over, you might get shot, you might get killed in any number of ways. Yes, it's scary when you think about it, but the cold hard truth is that life comes with risks and some of them, including this, we'll just have to live with.