The idea of erotic imagery being legal is based on the subjective of the viewer. So if it falls outside that viewers per-view, and it is seen as offensive by another, that then entails becoming unlawful. Because the other person see’s it, and judges it as offensive.
People can pretty much do what they want to themselves. Even though suicide is self murder. They get away with it, wherefore can the prosecution fall? Well, it is still unlawful because not all attempted suicide is successful. Which is good. Because you can still keep the person alive. And it is murder. Erotic imagery is till considered indecent as it takes only one person to see it that way.
The matter of erotic imagery still gives law enforcement to shut it down, because they can say in the public domain (i.e. the internet, the store) it is in the public eye. And with that, they can subjectively under the Three-Prong rule, take prosecution to it. And prove it is accessible/exposed within the public eye.
As for the age of consent or someone’s willfulness to participate in sex not against their will, has to do with two parties. And injury done to another person, making the act unlawful under that circumstance. Thus preventing abuse.
Wherefore erotic imagery has to do which is seen as offensive. Can you look at other people having sex? Like peeping toms? I guess erotic imagery makers can show what they want. And thus it’s out there. So it’s open to the peeping tom. Adults who consent to erotic imagery being shared is saying they are able to share indecent material (as is understood under the public setting and eye.) And with that, they can’t. Wherefore, if they do, It has to fall on the premise wherefore (i.e. a website, magazine, subscription, some property, etc.) On their own property. But, when it is seen under the public eye, it thus becomes unlawful. And that public eye can be flexed in so many situations.
Which the public eye is quite mobile. That it can perceive in any circumstance that something is indecent. That gives mobility and strength to the law to take it down. All it takes is an observer who see’s it is offensive. The person who views it may have more freedom. But the person who creates it, does not. Thus just by one observer, it can be judge indecent. And prosecuted. Which still means there’s room to it’s unlawful character according to the subjective that has more leeway under that Three-Prong measure.
A person might have freedom to subjectively look at whatever they want. In fact, you can see, sadly, what happened to Jewish people. Or any form of torture. And sadly, horribly, people who align themselves as racist keep those images for their sick reasons. Is it unlawful for people to view those images since they are offensive? It could be. But people preserve those images to take account of history. But erotic imagery, afraid that is not what it is meant, and for.