Well, if this is the case then the text should read "if you want to use a monster as a tribute for a card effect or summon, you can select and use a monster on your opponent's side of the field." But since it does not state that, I will stand by my stance that you MUST have a monster on your side of the field before you can use the effect of
Soul Exchange, regardless. The rulings totally contradict the card text and leads me to believe that rulings that contradict card text only suit their own purposes to make the card work how they want rather than the way the card was meant to be used.