So, what you're saying is they protect the value of a currency by devaluing it?
> it is not a conspiracy to enrich some cronies. without central authority, it cannot function as currency.
No, it's a conspiracy to tax the population without actually taxing them through devaluing the currency (aka inflation). Enriching some cronies is merely a side effect that keeps the bankers in line (and, more importantly, in the cartel) since they profit handsomely through fractional reserve banking and debt monetization -- neither of which is possible "without central authority".