Thank you for bringing this up. It's the old "immovable object" versus the "irresistible force" dilemma.
I would expect the Benevolent trait to trump the Malevolent trait, because the Benevolent trait has a reduced, specialized scope, i.e., it only applies in one's zone of control. It allows the Malevolent trait to apply everywhere else. It doesn't render the Malevolent trait 100% useless until all existing factions have the Benevolent trait. On the other hand, the Malevolent trait neutralizes the Benevolent trait everywhere, and for all races whether they achieve the Benevolent trait now or in the future, and so has a clearly larger scope. The antidote for the Malevolent trait is that all races must adopt the Benevolent trait. So when one achieves the Benevolent trait, something is guaranteed to happen. If the Malevolent trait is supreme, then achieving the Benevolent trait might result in no change at all. Achieving the Malevolent trait is unproductive ONLY when all other races have already inoculated themselves by achieving the Benevolent trait.
In other words, it takes much more effort to completely defeat one race's Malevolent achievement if the Benevolent trait trumps the Malevolent trait. That's my preference.
