It’s not working for piracy. This would seem to be even more difficult to fight than piracy since it can be done on a computer all by yourself without connecting to any other computer or distributing any files.
Again, the idea isn’t to render it physically impossible to occur or to stop it from ever happening. There’s probably not any law that fits either of those criteria. The point is to make it a crime. It shouldn’t be legal to make realistic nonconsensual porn of another person. If it’s discovered that you’ve done that, there should be legal consequences.
In practical terms even if it is illegal there is no reason you would ever be caught creating AI porn for personal use, as long as you create it locally.
I think it is an interesting question: why should something be forbidden if it doesn't directly harm anyone?
In my opinion, it comes down to people feeling unsafe because this kind of media is consumed by other people for (sexual) pleasure. A lot of people in our society had experience with sexual abuse and rape - especially for women the numbers are extremely high. If media with this kind of content is consumed by people for sexual gratification, it may make victims of rape feel very unsafe.
Maybe I can bring an analogy from my own life to clarify my point. I love wearing skirts regularly, most of them are mini skirts. I would feel very unsafe if I would know that one of my friends watches videos of upskirting, even if they are created by an AI. For me, that means that I won't feel safe around them. Of course you can say "well, but why are you scared of them; they aren't filming under your skirt, right?" And while I agree, I had my fair experience with catcalling: too many people in society don't respect my right to wear skirt the way I want them. If I would know a friend watches this kind of content, I would doubt if I can really be safe with them.
I think it isn't unplausible to assume that for a person who has been sexually abused, knowing that some people enjoy this kind of content would make them feel very unsafe. In case of porn, this usually is media we consume privately and don't share with others. So no - while I don't think the act of watching AI porn per se is harming anyone, the consequences for victims of rape absolutely do.
And yet we still put stop signs where no police cars patrol. Because people will avoid bad behavior for three main reasons:
They know it's wrong
They know it's illegal
They know they might get caught
Laws help with #1 and #2. If you're telling me the only one that factors into your moral calculations is #3, then you might wanna check to see if your soul is still under warranty.