Do you not think the Witnesses would also execute people for far less reasons than Muslims do if such a thing was legal?
I can just picture the look of insane glee on some of the Witness faces having learnt somebody tried a smoke, as they rush to find the biggest stone they can find.
The Witnesses have to settle for disfellowshipping instead which is like a delayed death sentance were it is God who will do the killing for you, in the meantime you pretend the doctrine breaker is dead.
Its also adviseable to seperate Islamic behaviour from Cultural behaviour of Islamic countries when critisising this religion, Female circumcision for example, whilst being practised by Muslims, isnt actually a Muslim doctrine, its just that the peoples whose culture practise such a thing, also practise Islam.