Can i ask, what do you win by mocking or say blasphemy about other people or religious leaders? What do you gain?
Freedom. Power against those attempting to impose their beliefs on others.
The wrongness of these killings can be countered by mockery. That is a legitimate way to fight such terror.
The mockery of the beliefs themselves serves a similar purpose: to distinguish the silliness of the beliefs and frame the discussion.
Also, not all art is a matter of what is 'gained'. Sometimes an idea just needs to be expressed.