A lecture is a one-way process, so the it's up to the student if the lecture is worthwhile for them or not. If it's not, they shouldn't attend. If no-one attend

A lecture is a one-way process, so the it's up to the student if the lecture is worthwhile for them or not. If it's not, they shouldn't attend. If no-one attends, the lecturer needs training/putting out to pasture. Like you say though, it makes sense for a class where you are expected to participate, since then you will be teaching and learning from the other students as much or more than the teacher. The problem here is you, the student, have become part of the value proposition of the class -- and the penalty against non-attendance is not the school penalising you for reducing your own learning, but a discouragement from reducing the learning of others, who the school promised a classroom full of smart peers.