I think it's unlikely that scamming will be the biggest opportunity in the long run, given how unsustainable it is. Mutually beneficial uses will predominate over time because that's the only way to get repeat users.
Unless an effective defense is developed, scamming can be continued as long as attempts at legitimate use are being made. Whenever activity ticks up, scammers will be attracted by it.
Scammers are fighting a losing battle against better security technology. They can only capitalize on insecurity. They cannot prevent people from developing and adopting more secure products/services/technologies.