Ex-NASA group plans private, crowd-funded asteroid hunter

Detection comes first

If money is no object then "yes", but it's generally hard to raise money for space projects so starting with on just one is pragmatic, and:

(1) diversion will "always" be a slow process - small amounts of thrust well in advance (sorry Michael Bay...) - so you need to see the impending collision a long time in advance - possibly years

(2) detection is an extension of things we're already quite proficient at - chances are quite good that Sentinel will work as expected first time. Diversion is a whole new ball game - a number of possible avenues exist but generally require exciting new tech and quite possibly we'll need several options eg for diverting a gravitationally bound hailstorm vs a big coherent lump. So both poorer bounds on problem and higher investment required

(3) the moolah for diversion will be more forthcoming if Sentinel finds a load of scary fellow-travellers

(4) maybe the Planetary Resources will invent the necessary diversion tech anyway as part of their NEO quarrying scheme - in fact maybe Sentinel will become their "bounty hunter" (unlikely since there won't be a perfect overlap between "things worth quarrying" and "things worth dodging")

"not being able to do anything about"

I plan to do a lot of running in circles and screaming.

Vladimir Putin?

If Dame Judi Dench can be persuaded to join the team too, with a couple of second-hand nukes they could sell the film rights, save the world AND make a huge protit.

Re: <40m

Yes, but there would still be a lot of other people around to go: "Ooooo, that was nasty", an effect you don't get with the big ones.

Small town with significant hole in it = Oopsie.

Total extinction = A Big Fat Hairy Deal.

We can address the concerns of the "Even one death is one too many" merchants after we've ensured the survival of the species.