What's the purpose?
There is none. Perhaps it would be better to say there is no logical purpose. Regardless of ones own views on the subject of the art for you to have the right to have those views the artist must in turn have the right to have their own views and make the art. Even if that wasn't the case where's the harm in someone seeing a dick or a vagina? Where's the harm is someone hearing what some people deem in their own subjective opinion as bad? I don't see any. And what about violence? As for that I can kind of understand having an age limit on however as long as one has the mental maturity to differentiate fantasy from reality then once again, where's the harm? I don't find that there is any.
BUT WHAT ABOUT THE CHILDREN?
Other people shouldn't have to make everything suitable your your children. If it's not intended for them and they don't have the mental maturity for it THEN DON'T LET THEM WATCH IT it's that simple. An artist should never have to change their art just to please anyone but themselves.
But I don't like when they do stuff I think is wrong.
Morality is a subjective concept. While many people can agree that some things such as killing are wrong there are some people who truly believe that it isn't wrong. Because of that morality cannot be objective. That being said why should someone change their moral opinion for you? It's pretty ridiculous thing to ask of someone.
What this all boils down to is things are censored because some people don't like those things. Not liking those things is perfectly fine for the most part so long as it's not inherently harmful. However expecting everyone to pander to your opinion is selfish. You wouldn't change yourself for a complete stranger so why should an artist have to change their hard work for a complete stranger?