I believe that most of the time, methods within a module should not screw around with their environment. However, if reporting to STDERR is seen as convenient, I prefer a module that will provide a switch to turn STDERR reporting on or off, defaulting to the off state.

When I encounter a module that insists upon spewing at STDERR, I add to my own code a method for redirecting STDERR to /dev/null, and turn it on at the same point at which I comment-out the uses of the strict and diagnostics pragmas.

I think that by providing the switch in your modules, you allow your user to operate more completely within TMTOWTDI space.