Wait, they "allowed" users to have their audio transcribed? Was this as a service, or is it just the b.s. corporate speak that FB always uses to hide what they're actually doing?
Facebook could theoretically have paid voice actors to produce the training data up front to eliminate concerns, and then never tweaked their models based on user data, but the results certainly wouldn't have been as good.
That all said, if they buried the opt-in, they deserve flak.
This sort of accusation could be overblown or underblown. Do we actually know the source of these recordings? Whose audio was recorded, under what conditions?