But why shouldn’t an act of generosity to someone who has mistreated you make you feel magnanimous instead?

The question isn’t so much what you owe to your brother as what you owe to yourself. Choosing to deny him a life-extending opportunity because he has been rotten to you would be understandable. It would also be ungenerous enough that you shouldn’t want to be the kind of person who would do it.

a) what the FUCK

b) that last paragraph REEKS of "technically you can get away with being a mean selfish horrible person, but you knowwwww you want to Do The Right Thing", which gives me the heebie-jeebies

c) kidney donation is not trivial and is in NO WAY a requirement for Being A Good Person

d) *possum scream*