Non-legitimate activity is not economic productivity.
Discussion
who decides what is legitimate?
many statecoiners will argue private transactions are not legitimate use of bitcoin block space, fortunately they will not be able to do anything about it
Scams and rampant speculation create noise. Noise creates information assymetry in the favor of the lazy schemers. Lemon market conditions arise, and the consumer cannot tell good product from bad. Left unchecked, productivity decreases in favor of creating more easy money schemes and less actual goods. Regulated markets begin looking more attractive, because real things are getting done there.