It doesn't take mental gymnastics at all. One could easily make the argument that market intelligence improves the allocation of capital and makes the world more productive. One could also argue that creating web apps for wealthy westerners is even less useful to society. One could note that being a subsistence farmer doesn't really contribute to anything or leave much of a mark for the future at all, and be ok with that too. All of these are just ways of surviving, and none of them seem particularly indefensible morally. You gotta do something to get by.

As for your link to Quora, that's a completely incomprehensible rant, just FYI.