One of the other crazy things about that impact, had it hit almost anywhere else on the planet, the extinction event would likely have been much more limited. Where it hit, modern day Yucatan peninsula, has and had a shit ton of hydrocarbons in the ground. Hitting there threw way more nasty stuff up into the atmosphere, greatly exacerbating the resulting impact winter, than it would have if it hit damn near anywhere else on Earth. Granted getting hit by a mountain moving at an orbital velocity is gonna be a bad day regardless, but it's surprisingly not always an end of the world scenario.
The rocks from space that concern me aren't the planet killers, we're unlikely to be surprised by one and would likely have years to decades, even centuries, to figure out a solution if we spotted one heading our way, and we have several potential options but haven't tested any of them. With enough lead up time just painting, or ablating, one side of the asteroid to be very reflective would shift it's course enough to make it miss.
The asteroids of concern, IMO, are the smaller ones, city killers, that we could miss and do miss all the time. We get hit by an asteroid that packs the punch of a nuclear bomb almost yearly, they usually explode over the ocean high up in the atmosphere so they go unnoticed by most. The one that blew out a bunch of windows in Russia a few years ago was one of those. That fucker was the size of a house, if had been either a bit bigger or a bit denser, iron instead of rock, or if it came in at a different angle, so as to be able to punch deeper into the atmosphere before exploding or even making landfall, Chelyabinsk would have been vaporized. As it was it exploded with the force of 500 kilotons, it was just so high up that the shock wave only had enough force to shatter windows. Imagine the Tunguska event happening over a populated area.