All this would do is that people will just import or download the games instead. People will keep playing whatever they happen to want to play. Net effect on "morality": zero. Net effect on German retail: negative.
Assuming they're genuinely worried about people playing violent games, it's incredibly naive to think that banning the sale of such games would somehow transform people into blissful model citizens (who won't shoot up a school). If they really wanted to make people more caring and compassionate, they could start by addressing the selfish and alienating attitudes endemic in the decision-making system they themselves perpetuate, for example, before randomly banning what could be argued to be a catharsis.