[bsder]

I have a fundamental belief that delivering a lecture is an active experience. I use and gauge student reactions to questions or comments to tell how well a class is receiving the information I am presenting. I also use it to pinpoint possible weaknesses of the class (did they miss the point of a prerequisite class, for example).

If I am not doing that, what's the point of a "lecture"?

Otherwise, you might as well read a book. It's faster than a lecture, likely more thorough, and not tied to a specific timeslice.

[haditab]

You may want it to be an active experience, but it will only be an active experience for those who choose to actively participate. Some students just don't learn that way and likely won't actively participate even if they show up to class. Those who want to actively participate will show up to class even if they have the option not to. There are other forms of getting feedback and interacting with students. Email and office hours for example. Also, I disagree that textbooks are faster. Maybe they are if you are an expert in the topic, but if you are not (and hence taking a course on it) in my experience the average lecture is still easier and quicker to learn from than reading the textbook (except for exceptionally well written textbooks).

I was one of those students who didn't learn by actively participating and I always felt like I had trouble learning in class. The school I did my PhD in started using online tools for some of the courses and I found that I learned way better when I watched the online lectures. A big issue I always had in class is when the lecturer explains something that is obvious to me in great detail, or just speaks slowly in general I find myself daydreaming and once I snap out of it I may have fallen behind and not be able to follow the rest of the lecture well. Online lectures at 2x speed are way more interesting for me and I almost never daydream. If I feel tired I can pause for a couple of minutes and stand up and stretch or walk around the room. If I miss a detail I can go back and replay it again. I would still attend office hours and email the professors though. What I learned from the online lectures also stuck with me much longer.

At the end of the day, students are paying an enourmous amount of money to learn, and I feel it shouldn't matter if the way they learn it by not showing up to class. Especially if they learn it better by not showing up to class.

[NineStarPoint]

If I could have when I was in college, I totally would have just watched the 100+ people lectures online. If I wanted clarification office hours were always more useful, and most of my teachers and TAs were very pleasant to engage in that context. Thankfully most of my classes were more on the 20-30 person scale (all of them in CS) where attending felt much more valuable. The few 12 person classes I had were undoubtably the sweet spot though, with enough peers around to make discussion interesting but much more engagement between students and the professor. Not that I expect most classes to be at that size, it would just be a better world if they magically could be.