Lizzy does not strike me as the kind of person who really believes that one should do what his friend suggests or advises, no matter the subject. In fact, she is not herself persuadable very much of the time! Yet, she defends Bingley's impulsivity against Darcy.

She also makes the comment about poetry killing the affection of a man once in love with Jane. I think she says this without thinking, to get her mother away from embarassing subjects, but she does defend her statment nonetheless against Darcy.