Then you have to diligently add every adult friend to that list forever, and there will be a gap between when you request their friendship and when you are friends with them and are allowed to put them on a restricted list.

Blacklists don't work in the Facebook model.

This would not be a blacklist. What Dylan16807 proposed would still be a whitelist. It would just use different criteria.

The reason facebook offers those filters is because a lot of posts are public yet facebook still offers a way to limit the audience.

Filtering the audience using circles is what Google+ did and proved to be unpopular.

Oh, I think I misread that, but it's slightly ambiguous - are we restricting blocking to specific people (Aunt Susan is uptight and shouldn't see my posts) or are we restricting post visibility to specific people? I guess Dylan probably meant the latter...

I disagree that the failure of Google+ means that nobody wants privacy settings, or in general that the failure of a business means that every single minor innovation they made was flawed. Google+ failed because of the network effect - a social network is only useful if it's also used by people you want to socialize with.

People consistently list privacy controls as among their biggest problems with Facebook, and circles solved that problem neatly once people figured out how they worked. You can of course replicate a circle with a user list on Facebook, but it's nowhere near as obvious.