Nowhere did I say anyone needed to be cheerful, only that ignoring basic social courtesy is rude. Going up the thread a bit, we're talking about "no greeting, no thank you, no smile" - now I can't speak for @coldtea but IMO all it takes to not be rude is one of those things. A single "hello" or "good morning/afternoon/whatever," a single thank you, literally any form of acknowledgement. Nobody is talking about making people dance or "actively smiling" except the people trying to willfully misrepresent others' opinions.

My point, and I think @coldtea's point, is that if you basically ignore customers, you're rude and shouldn't be in a customer service position. I grew up in the northeast US and it was rare to have any customer service interaction where you received no greeting, no thank you, nothing - precisely because it's rude, and most people aren't.