That was literally 12 years ago and is not in effect and doesn't even have a German wikipedia page and the federal court would have nicked. Ist alles von der Kunstfreiheit gedeckt!
You need to be more specific then, which law do you mean? Because the "Straftaten gegen die öffentliche Ordnung" is a whole section of the StGB which covers all sorts of things ranging from the prohibition of running an illegal online trading platform, to trespassing or leaving an accident. The closest is the Paragraph 131 which prohibits showing violence for the purpose of glorifying violence or to degrade the "Menschenwürde" (not sure what a good translation is).
Science disagrees on you with the harmless part. It is shown that violent video games desensitise people with regards to violence, just as violent movies do except there is a categorical difference interactiveness.
I don't like that fact either but to ignore facts because they don't mesh with my politics is bad.