The issue about this is, How is homelessness NASA's problem? its in the name, National Aeronautical Space Administration. And "well we all die at some point" is super deep and far-fetched because in the future, we will be able to extend our lifespan with new technology, and also work on stopping pollution (it may not be perfect) and building more homes. The DART program gives humanity a second chance in case of a collision course with an asteroid. I hope this answers your question.

Because this isn't star wars kumquat. A laser mounted to a 747 could barley shoot down a 5x5x5 foot ICBM warhead so what makes you think we can "blast" a 5 mile asteroid. The DART program is the single best way to DEFLECT, an asteroid, because there is no efficient way to destroy one.

I think 325 Million is a good price to put on more than 7 billion lives.

It will certainly not explode. Mars has similar to gravity to us, even less, this makes flight even easier.