Sounds good, yet real life is more complicated

  * many governments will call illegal whatever they want. Will you happily enforce governmental censorship?
  * even if government acts in good faith, there is no good definition of porn. At some point some person will have to look at a picture and *personally* categorize it as porn / not porn

(I guess first point doesn't make sense, since it's not a question of preference, you have to comply to at least one government if you want your company to survive)