Anti-German (German: Antideutsch) is the generic name applied to a variety of theoretical and political tendencies within the left mainly in Germany and Austria. The Anti-Germans form one of the main camps within the broader Antifa movement, alongside the Anti-Zionist anti-imperialists, after the two currents split between the 1990s and the early 2000s as a result of their diverging views on Israel. The anti-Germans are a fringe movement within the German left: In 2006 Deutsche Welle estimated the number of anti-Germans to be between 500 and 3,000. The basic standpoint of the anti-Germans includes opposition to German nationalism, a critique of mainstream left anti-capitalist views, which are thought to be simplistic and structurally antisemitic, and a critique of antisemitism, which is considered to be deeply rooted in German cultural history. As a result of this analysis of antisemitism, support for Israel and opposition to Anti-Zionism is a primary unifying factor of the anti-German movement. The critical theory of Theodor Adorno and Max Horkheimer is often cited by anti-German theorists.
I've always assumed it was from a deep rooted national guilt over the holocaust that makes them reluctant to voice criticism towards Israel.