Going back to the AOL model?
If you are worried about seeing bad things on Facebook/Youtube then stop using it!
If you are worried about your children seeing bad things, stop them using it!
If a significant proportion of "users" leave then Facebook/Youtube might have an incentive.
It doesn't take much effort to avoid offensive material on either of the big advertising networks.
Of course if either becomes a sterile walled garden of pre-approved content then I for one will go elsewhere. I still remember the AOL version of the Internet and will certainly not tolerate a curated internet.