I seldom write any reply on hacker news. But this time I feel I have something to say.
The fundamental question behind all these arguing is, what can be considered useful? In the other word, what we do, couldn't be considered a waste of life?
Philosophers have been arguing about this for 2000 thousand years. So I doubt there's going to an absolutely correct answer in near future. What I can offer, is just my personal choice.
Whether we like it or not, whatever we do, whatever we've build, good or evil, will vanish sooner or later. The human beings will extinct, the earth will become quite, the sun will extinguish. It's just matter of time. If nothing we do could make any sense in the long term, how can we consider something useful not?
Like any living things on this world, we, humans, are born to have many instincts, like to survive, to reproduce, to play. And when we don't obey these inner demands, we feel unhappy. So we eat, drink, sleep, f, and make money. However, that's because what we do is useful, or important, or has any meaning behind them.
Some people might feel happier when they can attain something that are useful* for others, which usually bring them more money, food, prestige, and many other things. But some might be satisfied enough by resolving some intelligent puzzles. As long as people don't end up in a crappy motel because they couldn't get their life in order, I guess these 2 attitudes towards life are both OK.