Professional Customer Service staff will always keep their feelings to themselves whilst in the public eye
I agree, but if they feel bad about work, this will inevitably impact on their motivation and thus their performance. The two observable behaviours are not mutually exclusive.
As to people showing ther feelings more, well society is a fluid and dynamic thing and it changes all the time.
Is it appropriate? Well that depends on your value systems and cultural norms, from which you will make a judgement.