"There is, I believe, in every disposition a tendency to some particular evil—a natural defect, which not even the best education can overcome." "And your defect is to hate everybody." "And yours," he replied with a smile, "is willfully to misunderstand them."

Is Wilfully to misunderstand them?

“There is, I believe, in every disposition a tendency to some particular evil, a natural defect, which not even the best education can overcome." "And your defect is a propensity to hate everybody." "And yours," he replied with a smile, "is wilfully to misunderstand them.”

Why does Elizabeth say I am perfectly convinced by it that Mr Darcy has no defect?

Elizabeth Bennet is making a comment in a general conversation involving Caroline Bingley, Darcy and herself, that Darcy suffers from no imperfections of character. She accuses him of feeling superior to everyone, literally she says to him that because of his feelings of superiority that he just hates everyone.