> If we look at existing laws, it should be. Depicting an underage person even when the actor is an adult is illegal, I think, in every country. So adult actress portraying a minor is illegal. So why not pixels depicting young girls should be illegal?

Due to that pesky First Amendment, this is not illegal in the USA. The USA bans child pornography under the rubric that producing or even viewing it implicates the perpetrator in the abuse of a child. If no actual child abuse is taking place, they can't ban it.

Cartoon images and the like may be banned if they depict an actual minor.