Fortunately there are groups that are doing just that: https://b612foundation.org/
Meteors large enough to detect are both incredibly rare, and are very difficult to deal with, and meteors too small to detect will hit you before you see them.
Not to mention that any detection will come with very large uncertainty bars. Suppose that you somehow discover that a ~500 KT meteor (Like the Chelyabinsk bolide - which was only ~20 meters across - good luck figuring out an accurate orbit for it) is an impact risk. The overwhelming majority of the Earth is covered with water. The overwhelming majority of the rest is... Not densely populated. And observations put it at a 0.5% chance of striking the Earth next year, with zero ability to predict which part of the Earth will be struck.
That's the most likely outcome of a detection program. Not '100% chance', not '90% chance', but a '0.5% chance of a rock that's scary only if you're in its immediate path'. Is that worth doing anything about?
The cost of all rockets ever launched is a pittance compared to NYC real estate
Also there is a project for a space telescooe spesifically designed to locate asteroids, its not that difficult or even expensive.
Even if you were gonna hit the meteor during significant downward trajectory (which seems unlikely), that would still have to be done at quite a distance from the impact location.
Also wondering when there was ever a "politically stable world without conflicts"
In 9 out of 195 countries.
And that's just all the publicly known ones.
Another issue I'm thinking is that I don't know the state of the art of meteor/bolide trajectory estimation (it's apparently very poor), so you'd probably need to fire a bunch of these (or a very large one) along an (uncertain) path hoping for it to affect the impactor.
So this is just more of the same problem: how do you fire a barrage of nuclear missiles over a region to stop an impactor in such a way that you're not mistaken for a madman starting nuclear war?
The asteroid needs to be pushed with a nuke, or another method, while it's still in deep space, months or years before it would strike. It would be many times beyong the orbit of the moon, millions of kilometers.
ICBMs are for ground targets, their "reach" is a thousand kilometers or so, they have no navigation or tsrgeting for space.
Instead a spacecraft like Rosetta would to be equipped with a nuke and launched on a normal space rocket like Falcon 9 or Ariane or Soyuz. We only need to produce a couple of them in case of launch failure, we don't need thousands of them like we have ICBMs. The launch would not look anything like an ICBM launch, it does not come back to earth.
Afik, there's a very abrupt limit on the size of an asteroid where if it's larger it will "touch" the ground and if it's smaller, it airbursts.
So if we could split the asteroid in 10, maybe we go from "completely destroy everything within a 100 miles radius" to 10 Chelyabinsk events.
'Impeding danger' means weeks or days at a minimum, so you have to use a nuke. It would be near moon's orbit.
If it's a bolide, it's in the atmosphere, moving faster than any missile. Its like trying to stop a bullet after it intered you epidemis - you already lost.
[0] I'm aware one of our best bets here would be a proper survey and sensitive enough telescopes/satellites actively looking for these kind of objects. And that there are some projects and programs along these lines already. It'd seem there's some more work to be done in that area though.
Am I wrong to wonder if a nuke would even do it either? I mean it's a ~solid rock that's capaple of surviving a pretty good beating from the atmosphere. What's a nuke going to do exactly? Are we hoping for redirection, or destruction or?
If your nuke can slow the asteroid from 20km/s to 19.9 km/s, then you need to nuke it 6 days before it hits earth.
There is a fascinating logistics and timing feature to this whole topic. Aside from global panic'd masses. There is a huge logistical difference between sudden and unplanned electrical grid shutdown and subsequent black start vs a pre-planned five minutes outage (assuming we can predict impact to five minutes). Another interesting electrical utility issue is the radiological damage from a melted-down nuclear power plant varies exponentially with time... There's a huge difference in expected damage between whacking the coolant pumps a month in advance vs a day in advance vs a minute of warning vs no warning at all just no coolant flow.
It seems the chinese were lucky like the russians while the Bronze Age folks were not so lucky.
So I guess we should invest more in asteroid defense.