And if skipping the lecture is a valid choice for learning then why does the professor need to be contacted afterwards? The professor already selected the information they felt was relevant and presented it in the fashion they felt was the most useful to the class. Your viewpoint only seems to make sense if the default assumption is that emotional information isn't a priority for the instructor but that doesn't jive with how a large swathe of the humanities and social sciences are often taught.
Reality check: so that you distinguish yourself from the slackers who did not came, because they did not felt like going. And there are always those.
Second, it is contra argument against "will not learn something important" argument. Visit teacher during open hours to learn that important thing. In all likelyhood, there is no massive thing to catch up with. Typically these are materials that are mean to make the issue of violence and rape less academic to students - seeing bodies makes it more real then reading about bodies. It is mostly emotional impact that is avoided.
Even if emotional impact is priority, emotional impact on person we are talking about is different then emotional impact on me. The material works completely differvently way for them.
Typically, the violent material is shown to students so that they break naive bubbles of how easy it is. People we talk about knows about it more then a student after seeing it.
> it limits the teacher's options because suddenly material that is meant to capitalize on surprise elements becomes a liability since it's unvetted
Teachers should not be making their students uncomfortable (let alone triggering trauma) by surprise. This is a consent issue.