The reason to go “gallivanting around the stars” is the long-term survival of our species. If we stay only on Earth, we are choosing certain extinction, full stop. Sure, we may last many tens or hundreds of thousands more years as a civilized species…but there are too many hazards that *would* sooner or later end human civilization (or humanity itself), just as has occurred several times in Earth’s past, whether from a supervolcano or from an asteroid strike. Surely you remember what happened to Jupiter with the Shoemaker-Levy comet strike.
If we choose to just stay on Earth, then we choose certain extinction. The only possible solution is to answer the human need to explore and spread.