

I don’t think that simile quite lands. Hindenburg worked as expected until its sudden catastrophic demise and hydrogen caused both the function and the failure. Zero knowledge proofs neither make cryptocoins work nor are they the reason why they don’t work.
A more apt comparison is something like saying levers are the technology behind this perpetual motion machine.
The design incorporates levers that fail to make the device function, but it’s not like levers are useless because of that.
What kind of a cost is low enough that eight billion people can pay it for their legitimate communications without burning the planet too much, but also high enough that a spammer with a botnet won’t bother to let other people’s machines pay the cost?