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.
I......I have to upvote this. Not because I agree, but because I don't agree. This opinion is completely unpopular with me. Therefore you get an upvote for being objectively wrong.