As professionals, teachers must be free to examine controversial issues openly in the classroom.
As a teacher for the last eight years I question this claim. All so-called "controversial issues" would by default include the freedom to examine unicorns, tooth-fairies, astrology, gods, reincarnation, resurrection, the holy trinity, and a myriad of other entirely evidence-lacking nonsense. Theses types of things can be dismissed outright and need not take up very much valuable class time (needed for the examination of evidence-based / science-based education).
Properly educate people in science, mathematics, physics, electricity, electronics, logic, , philosophy, history, biology, evolution, critical thinking, etc. and their improved critical faculties will hopefully take care of a goodly portion of the nonsense.
“The whole educational and professional training system is a very elaborate filter, which just weeds out people who are too independent, and who think for themselves, and who don't know how to be submissive, and so on -- because they're dysfunctional to the institutions.” - Noam Chomsky
“The smart way to keep people passive and obedient is to strictly limit the spectrum of acceptable opinion, but allow very lively debate within that spectrum....” - Noam Chomsky