Willingham’s purpose is to bring awareness to the fact that people may think they multi-task well, but they will still be distracted and miss important details.
Willingham’s audience is people who can drive, study or multi-taskers.
I would say that Willingham’s stance would be more towards the side of not agreeing with multi-tasking, but he does not completely cancel out people who may believe that it works in some situations, such as, say listening to music while studying.
I believe that this op-ed is convincing and persuasive because Willingham uses many surveys and other evidence to show the audience real life forms of how people feel when trying to multi-task and if they are successful or not.