I'd say it would be a problem if half the class just doesn't show up, figuring they can just watch the lecture online later. Some professors think this will make undergrads lazy about showing up to class, and more likely to fall behind.
How is that really different from half the class not showing up, figuring they can just read the lecture notes and text book later? If it makes the students lazy and they fall behind and fail, then those students have learned a valuable lesson for next time they take that class.
