Don't get me wrong, if you have a good jam or preserves it's totally fine on a sandwich, and I wouldn't turn my nose up at it. However, peanut butter doesn't really need the help, and the extra sweetness from jelly is totally unnecessary. Toasted bread and peanut butter is all you need for a quality simple sandwich.
Good post. This IS an unpopular opinion. I really want to downvote you because I disagree, but I want to upvote you because you clearly understood the assignment.