scheme organizers
Who are these "scheme organizers"? The devs? The core team? The first investors? There is no such thing in Bitcoin.
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scheme's economic activity
The "scheme's economic activity" is exactly what you describe as ...Quote
funds brought by the participants themselves.
... because Bitcoin is most similar to a barter community. It works only if it's used. But it doesn't need "new participants" nor growing value flowing in (as you seem to begin to acknowledge
).