As I am sure Airbnb is aware of by now, a great many if not most hosts do not want compulsory Instant Book. If you can't turn it off and decide that you don't want to go through with hosting unless you can, I suggest finishing the listing anyway and just snooze it. Then contact Air and tell them you are happy to make the listing live WHEN they change their minds about compulsory Instant Book. Some hosts finish their listing and just delete it when they realise IB is not optional, I think it is a pity to miss out on available and keen hosts.
If hosts did this instead of deleting their listings maybe Air would see just how many sleeping listings there are, waiting for IB to be turned off...
All the best.
Sandra