Would it really be much less expensive and take less time to build asteroid defense systems (I almost typed "missile defense systems") which require us to deal

Would it really be much less expensive and take less time to build asteroid defense systems (I almost typed "missile defense systems") which require us to deal with space than just to start getting better at getting into space anyway? Especially since most, if not all, of the technologies listed in the article would be put to better use for transportation (of either humans or goods) rather than as destructive ends (but such is the folly of human nature, I suppose). Planning for an asteroid strike strikes me as fear mongering, especially without being able to do anything "unless people see the asteroid in time to plan for it". Being resigned to a fate of having to continuously defend doesn't sound good either. I'd rather consider the possibilities for mankind's future as provided by getting off this rock than wallow in the status quo that merely deflecting an asteroid would provide.