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The fee is for executing the collateralized convert contract, which is not something regular users should do. There is no fee for using or buying HBD, or even the regular convert contract (HBD to Hive).

the problem is, the game to generate HBD is not on demand.

The only reason to have a stablecoin is " on demand".

5% fee does not get in the way of that. Usage and issuance of a stablecoin are completely separate concerns.

I would not say the 5% are insurance. If the time horizon for avg price goes bigger the fee becomes useless.