As a professor, I want my students to think for themselves and to not completely trust what I tell them. I am not an authority over their opinions—I can only present evidence and arguments. There are no scientific authorities. Every scientist making a claim is expected to support it with evidence in peer review. Although well-established science is extremely difficult to refute because it entails large amounts of evidence collected over time, no scientific claim is immune to the potential to be rejected, disproved, or replaced with ideas that are better supported by evidence. No scientist is entitled to safe space for poorly supported claims, including in the classroom.
I try to follow the scientific process in my classroom. Although students in the classroom are unlikely to overturn prevailing scientific views, encouraging them to express their doubts and raise questions can make the process of learning mimic the process of scientific inquiry. I want students to express reasonable doubt and to criticize my claims. Furthermore, I think that students learn science better when they confront ideas they do not yet understand, with open minds. When students express doubt in a scientific finding because they do not understand it, that expression can help the teacher understand the nature of their misunderstandings. When I discover inadequate understanding I can take steps to clarify the concept.