Politeness. Good or evil?

Hello everyone. I am relatively new in Western society, and one thing makes me confused almost every time: politeness. For example, when an employer says "you make a big mistake" and at the same time says "you a good worker". Or when random people's constantly smiling to you, without any reason. In my opinion, based on the culture in which I was born and raised, it makes social communication more unclear and provides some misunderstanding. In my opinion, brutal honesty is better than politeness because it gives a clear message without double meanings. Did you agree with that?

Politeness. Good or evil?
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