Cameron - or the Daily Mail - clearly thinks the internet works like a school library, where you can check any individual book for itself, leaf through it and make sure it's clean - or if it's problematic, put it in a special locker or just suppress it. There's no recognition that sites change over time, the content of any one site grows as it's used, and that links are part of the lifeblood of the web. If all links to let's say IMDB or Youtube suddenly went blank on most pc's, phones and devices in the UK because a small fraction of the material these sites host isn't 'family friendly' and they had refused to remove it, quite rightfully refused, then many other spots that linked to those sites, but not to the "dangerous content" at all, will lose value, or even become impossible to understand.