On these questions where we compare fish to human, there are often so many different things involved that it really just doesn't apply. We have discovered lead does damage human brains but that was only after many centuries of using lead for water pipes as well as dozens of other things. So now the question whether it is safe for fish. Do I want to risk my fish becoming crazed animals and attacking me in the middle of the night? Or do I want to make my tanks work using the easy methods that have been used for a hundred years?
I go with the easy and will throw the fish out if he orders a gun or knife online!