Think of other places Imagine you live in a heavily censored country like North Korea. No freedom of speech, no news from the rest of the world, so many limitations on how you live your life. Break the laws of this censorship and risk imprisonment or even execution for something as simple as trying to find out who the leader of a foreign country. We know that governments like to push their boundaries and though it would be slow and go unnoticed eventually all expression would be snuffed out in places of a long period of time.
Protecting your child from what you think is deemed inappropriate is your duty as a parent not something the mature population of the world needs to be constrained by.