Oh look, a trope I actually hate, being shut down by a woman I love!
So great! Go Emma Thompson!
God, I love Emma Thompson! This particular trope is rooted in the idea that, whereas men have a strong, mature sense of morality in the abstract, and therefore act selflessly for the greater good, women are childlike and incapable of higher-order moral abstraction, and therefore care only for what affects them personally. (Yes, I read Carol Gilligan in college and it made a big impression.)