MeFi member ChuraChura talks about how she teaches anthropology while also carefully navigating existing student belief systems.
So with this as my student population, coming in and laughing at their silly beliefs would alienate a significant chunk of my students - which (as well as making for a semester of dread and aggression) would really impact my ability to teach anything! And it's an awesome class! I talk about primates for about 5 weeks! And they play with bones! And hear about genitals! And Alfred Russell-Wallace! Cool stuff!