Earlier quoted context omitted.
> What externalities are you talking about? Economic activity. Switching from free banking [1] to a centralised currency made trade easier in America which increased the amount of trade. It's why monetary unions work [2]. Bitcoin, similarly, has enabled certain modes of trade that previously didn't exist. [1] https://en.wikipedia.org/wiki/Free_banking [2] https://ciaotest.cc.columbia.edu/olj/cato/v24n1-2/cato_v24n1..…
I think that is more of consequence resulting from lower transaction costs, rather than an economic externality. That said, I understand the definitions of externality is changing in popular usage.
An externality is "an indirect cost or benefit to an uninvolved third party that arises as an effect of another party's (or parties') activity" [1]. If Visa reduced its fees, the merchant's additional profit is an externality.
> understand the definitions of externality is changing in popular usage
Third-party economic consequences have always been the definition [2].