> A ban would legitimize its utility to people skeptical of central banking

i.e. a tiny irrelevant niche. I don't think banning bitcoin is a good idea, but a ban would be highly effective because nobody cares enough to risk fines or jail time over something they have no use for anyway.

There's a simple way to ban bitcoin. Govts already regulate the banking and payment companies. Govt can compel them to not allow/facilitate exchange of bitcoin for fiat currency or vice-versa. Without banking/payments infra supporting such a conversion (only hand to hand cash transfer and exchange conversion by person to person transfers would be possible) which will be very small and network will be dead soon. But obviously govts didn't do that and hence bitcoin has so much usage and hence such high value.

A billion is not much once you get to Pentagon scale budgets and is probably cheaper than going to war with Iran.

It's not really an option. The hard (and VERY low) cap on transaction volume is a joke. If you think a Bitcoin is actually an option for actual banking for actual people (not just the current set of a few thousand gamblers), you are delusional. The current financial system DOES process more transactions in a millisecond than Bitcoin CAN in a week.