[cgmorton]

But then you can easily, heck trivially, argue that people should be forced to exercise or to eat a particular diet that makes them more productive. Look, more goods and services are rendered! It's a public situation!

People should be forced to live within 5 miles of work, because they're not being productive during their commute. Also, HackerNews and reddit should be forcibly taken down because of their contribution to idleness at work.

[confluence]

You forget about second order effects once again - HN/reddit facilitate low latency, high scale, high signal communication between millions of people everyday - that's a net positive.

In terms of diet, we tax cigarettes, alcohol and drugs (indirectly) - food that is net negative on society should have their negative externality priced via taxes.

It's pointless banning them (e.g. enforced diets) - see prohibition - leave it legal and tax to cover costs.