Some sectors aren't "productive" on their own but still necessary. Railways basically never pay for themselves by fares paid by (mostly) workers out of post-tax income, but the value they bring to the economy by enabling economic activity is worth it.

Roads, education, healthcare, much of these things would either be unprofitable or unaffordable if they have to be self-funding. But they bring social value even if they don't make their own shareholders rich.

The commenter I was replying to was not talking about social programs. He was talking about a command economy.

I’ve never understood why this argument wasn’t the first thing economists bring out as a counterpoint to MMT. The entire thing hinges on a central planner knowing where to spend money. Gee… we’ve seen that work out so well in the past.