When I was an undergraduate, I had many professors who were open to debate and encouraged students to disagree with them. I had 2 professors (Keith Gallagher and some Jesuit theologian whose name I forget) who responded negatively to disagreement from their students. I received As and Bs in every other class, but Cs in classes from those 2 professors, seriously damaging my GPA.
So, it only takes a small number of such professors, to make the rational decision by a student be to always agree with the professor.
Sorry, Gallagher is a CS professor. How could he have graded you poorly for disagreement? I can see how that can happen in the social sciences or humanities but it isn't clear to me what that would even mean for a CS prof.
Link.
Given the positive reactions, I think the professor seeded them with a positive impression of the site's content.