This is a bit dismissive of anything that considered valuable RIGHT NOW.
Gone are the humanities, the social sciences, the histories, the ancient linguistics, all of which depending on who you are could consider to be play around, while the rest of us serious people work for a living building software.
I left a math PhD program due to health reasons. Looking back, none of my reasons for studying math was for the potential usefulness of the ideas I was studying.
It was all for social status and personal play reasons.
Investing in ideas that may pay off in the future is an excellent idea. But except for the cream of the crop, few people will actually have their useless knowledge turn into something useful.
I suspect many people push this point about potential returns because they want to "get paid to play" as well as participate in a system that allows them to gain social status. If they convince others to support them using some argument about useless knowledge being useful, then they can continue in this way.
My only point is that I wish more people were open about that. Yes, research pays off, but if you are in a position of being able to learn lots of "useless knowledge," you are already doing well in terms of health, intellect and status. Don't bemoan too much about your life.
Gone are the humanities, the social sciences, the histories, the ancient linguistics, all of which depending on who you are could consider to be play around, while the rest of us serious people work for a living building software.