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.
Better unpopular opinion: US-style peanut butter is disgusting. It is sweetened and has an off-putting structure. European style peanut butter is way better.
More popular opinion: the best topping for peanut butter is sambal, which is an Indonesian style chilli paste