Disagree with your friend big time on this one. Knowing the twist can make a rewatch way better because you catch all the little clues you missed, like in The Sixth Sense when you notice Bruce Willis never talks to anyone but the kid. But that is different from someone just blurting out the ending before you have seen it once, which does kind of kill the first watch. Maybe the split is not about brains handling tension but about first time vs second time. Spoiling a movie you have never seen takes something away, but knowing a movie you already saw just adds a new layer. So idk, maybe both your friends are right for different reasons.