It goes beyond just the strong victimising the weak. Bullies are not strong and their victims are not inherently weak. Strong and weak are relative terms and someone very weak can bully someone very strong if they take advantage of certain circumstances.
Bullying is just opportunism where intimidation and exploitation take the place of developing real power.
Aikido should empower people to avoid this kind of opportunism. Bullying within Aikido sounds like some kind of Budo HIV, infecting the very thing that should be stopping it. Not good for an art that must be practised honestly.