Originally posted by dadudemon
Because it's a sore spot for Madara and his Brother was almost as powerful as fully powered Madara. (minus, EMS, of course)
Madara would be shocked, sure, but that wouldn't make Kabuto a "madman". His brother poses no real threat, and would not be hard to control, so I would not only call summoning his brother a normal choice, but maybe even an underpowered one.