I read jajvirta as saying that the occupation itself doesn't produce positive externalities for mankind, unlike productive work in physics research or something.
Productive work in physics could produce negative externalities if humanity cannot be trusted with new physics results. Hell, even math education could produce negative externalities!
Here's our place to discuss Less Wrong topics that have not appeared in recent posts. Have fun building smaller brains inside of your brains (or not, as you please).