Man, I've been in large lectures where there 200 students in a classroom and the professor tolerated completely inane arguments to try and teach just one student the material.
If you're in a class and you don't think what the professor is saying is right, either ask a question or write a note so you can follow up on it later.
Not once in my undergraduate career was I expected to turn off my brain and go on cruise control just because the guy down in front was an expert.
Honesstly, I feel like my whole benefit of my academic career was taken from sitting in a class, not understanding what the fuck was going on and then struggling to understand or contradict what I was being taught.
In lower level courses, where straight up lectures are more common, professors are more inclined to simply teach the facts instead of trying to create a(n unmanageable) discussion between 50+ people. Which is understandable. And they (usually, at the beginning of the semester, at least) stress that they have office hours or are available at other times if someone wants to continue talking about a topic for whatever reason.
But these are my experiences, maybe I've just been lucky?