When the scientific method yields discoveries that imperil people’s lifestyle or worldviews or impinge on corporate vested interests, the public and political response can be anything but favorable. Sometimes the response slides into overt denial of scientific facts, although this denial is often claimed to involve “skepticism”. We outline the distinction between true skepticism and denial with several case studies. We propose some guidelines to enable researchers to differentiate legitimate critical engagement from bad-faith harassment, and to enable members of the public to pursue their skeptical engagement and critique without such engagement being mistaken for harassment.