>why does anyone have to justify their lives by doing something to improve the world?

There have been a few replies in this vein, and I see where you're coming from based on the way I phrased what I was saying.

I'm not arguing that anybody should be forced by some external entity to do anything. I am advocating for a person in this situation to attempt to cultivate a passion/greater purpose because I believe it's something we need to be fulfilled. The man in this article designed a life for himself that was free from labor, but ultimately unfulfilling in many ways.

And if you need to find that passion, looking to improve society in some way is a great place to start. I can think of a few things in that vein that I would consider focusing on if I was in such a situation, and none of them are as far reaching as "make humanity multi-planetary."