the punish everyone to punish one technique

this is my little rant about those who punish everyone just so they can punish one, and why it is, while effective, immoral. one example of this is when a teacher says that no one can leave until someone admits they did something. this method of punishment is quite effective, because it applies peer pressure on whoever it was, and also apeals to their morality to stop the punishment of all the other people. So long as they feel morally obligated to admit they did it before it becomes akward for anyone to say anything at all, this works. But, the immorality of this method lies within the requirment of the criminals morality to stop the punishment of all, and the fact that the criminal did not create the punishment affecting all the innocent people. As an extreme, i offer the hypothetical situation in which an authority figure uses their power to kill off everyone until someone admits they killed that they kill a person.