Most classes shouldn't have mandatory attendance policies. If you can learn without listening to the teacher, you shouldn't be penalized for it. And if you can't, you'll be penalized when you take the tests.
Really, it should be up to the student. If he thinks he can learn without going to class, he should be allowed to. Then he can be judged by whether or not he really did learn the material.
It seems like just arrogance for professors to require for you to listen to them. As if they were the only way for someone to learn.
I will make an exception, though. Any classes that involve group discussions, or something of that sort, in which not attending can hurt people who did attend, attendance should be mandatory.