That person is an idiot a true emberasment to Germany, one of the most psychologicaly enlightened countries, producing reknowed psychologist(Frued anyone?)
There is no basis to this law, nothing supports it. All research conducted on game cruelty and real life have proven to be negatively correlated. Meaning that they have almost no effect on psychologically stable people, most of understand that that violance is animated and that we shouldnt repeat it. Now for games to effect a person and cause him to repeat that behavior would mean that the person either a) had a traumatic past(child abuse), or

was just psychologically unstable genetically, the games most likely didnt make him so, they just reenforced an already procurrent disposition towards violance.
And its not like this is the only law proposed that will effect our freedoms as gamers and as citizens. Anyone heard of Network Neutrality and what might happen to the Internet soon enough.