Lol, are you serious?
There are specific rules in place regarding the deletion of posts and threads, specifically helpful ones. There are several reasons why needlessly deleting posts is not allowed, one of which pi mentioned. If a user breaches the rules it is up to moderator discretion on how to deal with it. For future reference if you have genuine reason for deleting a bunch of posts it is advisable to contact the moderation team before doing so.
And what does 'no exam discussion' mean on a persons profile?
Users who did not wish to see the exam discussion boards and posts made in them were advised to contact the moderation team. They were then placed in a specific user group entitled "No exam discussion" which made these boards invisible to them.