Thank you for sharing your opinion! :)
I believe otherwise. I think if the function mutate an argument it is considered impure.
Just consider the scenario:
I gave the calculator ( 2 + 3 + 5 ) and it gave me back 8 instead of 10.
What happened? It did something "unpredictable".
The 4th example mutated the arguments. and did something "unpredictable". Therefore, I believe it is impure.