But you could still see sites about bestiality or gay clubs. This is the avenue taken by word-based filters. Hundreds of words are put into a list, and sites registering that word are blocked. Even so, there are so many flaws in this system that it deserves very little ink. Vulgar slang helps perverse sites dodge the obvious words.
Intentional misspellings dodge some filters.
Pornographic sites in non-English languages litter the superhighway. And many sites don't even have words just pictures. Too many leaks make them ineffective. The only way to allow access to all of the non-offensive sites on the web, while blocking all of the undesirable sites, is to single out each offensive site and block it specifically. This eliminates the confusion of keywords, nullifies the need for ratings, and requires a much smaller database than a quality pass-through list.