Those absentees...!

From a recent conversation,
Question:  "there are about ten students who are constantly absent from certain lectures. what's the strategy that's employed to mitigate this..."
Response: "No strategy, No plan. We can send a warning letter about a student not being allowed to sit for the exam if he does not meet the 80% attendance criteria..."
Which begs the question, hopefully will be answered by the students themselves;

1. What should you do with the students who are constantly missing lectures?
2. Should anything be done at all to get these students to attend lecture?
3. As adults, should they not be allowed o decide for themselves whether they want to be part of a particular lecture or not?

What do you think?