What does critic Kenneth Moler mean when when he says that the character of Marianne is "a sermon on the dangers of ill-regulated sensibility"?...

This quote refers to Marianne's attitude which is
completely dissonant to that of her contemporaries in Regency England. She is a woman
who is outspoken, opinionated, challenging, stubborn, and dead serious about what she
expects of herself. She has all the qualities that maybe are expected of a gentleman,
instead of a lady.

To her peers, she is trouble. A woman is
supposed to be quiet, undisturbed, pleasing, eternally dependent, and subservient. She
is everything but these things that are characteristics that mothers should have taught
her daughters.

Therefore, being a sermon on the dangers of
ill-regulated sensibility is the same as saying that Marianne is the epitome of
imprudence, lack of class, lack of manners, and lack of good behavior according to the
outdated expectations bestowed upon women in Regency England.