It is more specific than that. Mr Cameron has recently upset quite a few very influential bigots over the gay marriage thing (something to be applauded IMO) and is now trying to sweeten them back up ready for the next time he needs their vote or party donation by tackling an issue that they care about but which won't overly irritate too many other people. The porn access issue is a gift to him in this respect.

I'm sure he knows the measures are going to be ineffective, if he doesn't he needs to sack a few advisers, but it is important for him to be seen to be "thinking of the children" on this issue.