Bear in mind the specific case being discussed is for B2 buckets, not Backblaze personal backup. Anyone using the B2 interface directly I would hope could be viewed as technically competent. If they can distinguish between the two on their end, it would make sense to provide it as an option for B2 at least.

The best way to deal with 'are you really really sure' is something like send an email with a link you have to visit as confirmation as that breaks you mentally out of the 'keep confirming without thinking' cycle which we are all at least slightly prone to given the number of confirmation dialogues we all see these days.