Your comment is quite disingenuous. The major ISPs offer parental filters that can be used to block many different types of content, and specific websites, but they are not the default: they are opt-in. The default (opt-out) filter with BT for example is "Light"[1], which only blocks the content you'd expect to be blocked by a "family-friendly" filter. To block Media Streaming, Fashion, Sex Education and File Sharing you have to opt-in to "Strict"[2]. If someone opts out of the default ("mandatory") filter they are opting out of a porn filter, not a sex education filter.

[1] http://i.imgur.com/5IN6VGC.png [2] http://i.imgur.com/PinT3xy.png