Whilst it is Facebook who is banging the drum here about the potential pitfalls of the OS update, people need to stop and remember that this doesn't just affect Facebook, it will affect EVERY free app in the app store that relies on advertising so it can be free. Stop and think how many free apps you have on your iphone or ipad and then stop to think that when the update roles out and you say 'No' to these free apps wanting to push advertising on you, the free app will instantly lose it's revenue from the advertisers and if no one is watching the adverts, the advertisers will stop providing money to app developers. Then the app developer will no longer be able to provide updates for their app because they have no money coming in. So, do they just up and quit, leave the app platform and go work on something else leaving the app users high and dry or do they switch to a subscription system which due to Apple app store rules means they are forced to use Apple's pay system.
People are being too blinded by Facebook to see the actual problem that Facebook is trying to address which is, if users opt out of the free apps advertising, the app will not be able to support itself because the advertisers will leave which means how does the app developer support themselves? by subscription and who provides the subscription service, Apple of course because they do not allow other pay/subscription systems to be used in the app store. Therefore as a direct consequence of Apple's actions, they will be forcing developers of free apps to move to a subscription based service which only Apple is allowed to supply, a service that Apple takes a monthly percentage from.