Mockery can be cruel, and even gentle mocking can be irritating or even harmful if it's very repetitious. Mockery is not always appropriate, or even truly funny. Mocking others is not an especially important activity or an especially important form of humor.

Even so, categorical prohibitions of mockery (in society, in particular workplaces, whatever) are truly and obviously joyless propositions. Maybe they're warranted in some contexts! But to say 'there can be no mockery' is indeed inherently stifling.