I just can't see how that can be true - 'we're going to murder you all, but we're going to do it with good manners because otherwise people will think we're bad

I just can't see how that can be true - 'we're going to murder you all, but we're going to do it with good manners because otherwise people will think we're bad'?? It seems way more likely to be 'cargo cult' type learning where something worked for centuries and so got formalised and taught rigidly? Any good sources on this, it must have been covered on AskHistorians!?