What's wrong with the population in Berlin?

The majority of Berliners - and Germans - don't think involvement at the level being asked is appropriate. The soldiers are reflecting the citizens' wishes. Germany's stance, as reported by the media, is that aiding Ukraine in the ways being discussed could lead to broader war and additional conflicts. Given the nation we're talking about, I'd say they know.

Germany sits along Russia's border; we have no expertise over them. Not every nation on the planet is quite as impetuous or bloodthirsty as the US.