As much as it may hurt you to punish him, it's somewhat necessary. After the punishment is over, then if it worked out properly, you won't have to re-punish him for the same or similar behavior again. You may not even have to punish him for a completely different behavior for some amount of time. We all have to do things that we're not always comfortable doing for the better.

Although child developmental psychology is not my area I'm studying in, I do think that a parent should establish their role as parent and not as a kind buddy or a friend. A parent is meant to be a parent but ideally a parent is meant to be a good caring parent. At the same time, I think it's necessary to avoid being too passive and too much like a drill-sergent. Kids are young and they're going to explore their world, and part of that involves getting into nonsense and things they shouldn't.