Has SpaceX thought about landing on an asteroid, and deploying technology that can either redirect or disassemble an incoming asteroid to avoid or lesson the asteroids impact on earth?
Except perhaps for extracting volatiles from asteroids for use as fuel or oxidizer for missions to Mars, Elon Musk, the founder and CEO of SpaceX, doesn't see much potential in asteroid mining. He said in an interview with the British Royal Aeronautical Society, "I'm not convinced there's a case for taking something, say, platinum, that is found in an asteroid and bringing it back to Earth."
With regard to planetary defense, there is no indication that SpaceX sees this as their job.
I read NASA's idea's and they seem to be set on blasting them.
That certainly is one idea with regard to planetary defense against hazardous asteroid impacts, and it is the only option if the time frame between discovery and impact is short, where "short" means anything less than a decade. All other options require multiple decades of continued action.
That said, this is not NASA's sole idea with regard to planetary defense, and it is not NASA's sole idea with regard to asteroids in general. NASA's OSIRIS-Rex spacecraft is currently en route to 101955 Bennu with the intent of mapping the asteroid starting later this year and eventually returning a sample to Earth in 2023.