If 1 in 100 humans could run up to 100mph you bet your ass there'd be laws against doing so around other people; it's a safety concern. Hell, even now running in most indoor or crowded areas is, if not illegal, at least considered bad behavior and may get you reprimanded or thrown out.

Some people claim to have a photographic memory. Supposing this is true, is it illegal for these people to look at copyrighted material because they may reproduce it later from the copy in their head? Of course not, it's the actual act of producing that copy that isn't allowed.

Of course, we're not talking about a computer program that stores a copy of an image and reproduces it later (that's called an "image encoder"), we're talking about is a statistical software that identifies common patterns in images and associations between those patterns and human language descriptions of the images containing them. It doesn't store or make a copy of the images it learns from, and it should only be able to reproduce images or elements of images that are overrepresented in its training data. Like any other software tool, if someone manages to use it to make an unauthorized copy of someone else's work, whether it was present in the training data or otherwise, then the user has infringed the other person's copyright. The only real argument you could make is that distribution of a trained model constitutes distribution of a tool aimed at assisting users in unlawful copying, but IMO that would apply more easily to wget than StableDiffusion.

Copyright laws were made to encourage and promote the creation and practice of useful arts. Applying them to stop the creation and adoption of a tool that would make humans far more efficient in the creation of art is backwards.