Originally Posted by
stimpy
It's not to force the staff to greet the pax, it's to "force" the pax to greet the staff. One of many psychological benefits is that the pax are less likely to be belligerent if they exchange a kind greeting with the staff. That's sort of why the custom developed in most cultures centuries ago.
Ah, sorry. I get you now. But still, I would agree with
Richelieu,
SG and others: you do not need to show your BP to answer a good/morning/afternoon/evening/Welcome on board. And if you are not going to answer this, you probably still would not answer even if you had to show your BP anyway.