Denouncing the ISIS as un-Islamic or "bad" Muslims is counterproductive, especially if those who hear the message have read the holy texts and seen the endorsement of many of ISIS's practices written plainly within them.
After all the atrocities we see, if Muslims go about their lives, they stand condemned by those who demand that Muslims “speak out.” But if they do speak out, they can expect to be told that short of declaring their sacred texts invalid, they are fooling themselves or deceiving the rest of us.
Catch 22, but a sure case of its not like other religions. It needs to be criticized