Has he lost his ability to hate?
Nope, he still has the ability to be a jackass
I find most older people either become sweeter in old age or bitter in old age and typically it boils down to how they coped with the trials in their life. The person who finds the good in hardships and disappointments learns to cope better than the ones who just become more harsh and critical.
It seems obvious which way Ebert handled his challenges because he seems to be a very bitter man.