Stable Diffusion is developed at LMU Munich and this particular line basically paraphrases § 184 of the German criminal code, which makes it a misdemeanor crime to put porn in places reachable by minors or to show porn to someone without being asked to do so, among other things. I dunno why they felt compelled to include it though.

Regarding your examples, most of these are technically criminal in Germany, because the only legally safe way to have a place not-reachable-by-minors means adhering to German youth protection laws, which you're not going to, just like every porn site, Twitter, Reddit etc.