People who turn a blind eye and let evil things happen can hardly be considered good. Nazi Germany actually purged a lot of the good people internally before going forward. They brought the guillotine back as a punishment just for them. The "Good People" this sign is referring to are just the sheep. They went with the flow and kept their heads down in order to survive. They survived at the price of their souls (metaphorically, I'm not implying they all went to hell just for being cowards).