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One of the characters that Austen mocks and presents as being the most harmful to society is Mrs. Bennet. Austen constantly paints her as having a complete lack of understanding of propriety. She frequently acts improperly in society, such as having the audacity to announce to Lady Lucas that Jane will soon become engaged to Mr. Bingley. The impropriety of her announcement is in the fact that she announced such a thing in Mr. Bingley's own home at his own ball when he was in earshot, well before Mr. Bingley had ever asked for Jane's hand. Austen uses this outlandish behavior to mock the type of person that Mrs. Bennet is, for it's quite common for people to lack all understanding of decent behavior and decorum.
Not only does Mrs. Bennet act improperly, she is also described as having a "weak understanding and illiberal mind" (Ch. 42). By "weak understanding," Austen means that Mrs. Bennet understands little about the world and is even poorly educated; she is so ignorant that she even fails to recognize her own poor behavior. By saying that she has an "illiberal mind," Austen is calling Mrs. Bennet "narrow-minded, ungenerous, [and] selfish" (Pemberley.com, "Notes on Random Topics: Liberal"). Mrs. Bennet certainly is seen as putting her own comforts above anyone else's. For example, when Lydia runs off with Wickham, Mrs. Bennet's response is to remain tucked away in her own room the whole time, fretting. As Mr. Bennet sarcastically observes when he returns from searching for Lydia and Wickham in London:
This is a parade ... which does one good; it gives such an elegance to misfortune! Another day I will do the same; I will sit in my library, in my night cap and powdering gown, and give as much trouble as I can, -- or, perhaps, I may defer it till Kitty runs away. (Ch. 48)
Again, Austen uses Mrs. Bennet's humorous behavior, as well as Mr. Bennet's humorous response to her behavior, to mock individuals who behave selfishly.
The danger in Mrs. Bennet's impropriety, as well as in her lack of education, narrow-mindedness, and selfishness, is that her character not only affects her, but everyone around her. The greatest danger is that she is raising her three youngest daughters to behave in the exact same way. As Elizabeth frequently points out, Kitty and Lydia were in danger of becoming the most ridiculous flirts and, more importantly, of ruining their entire family's reputation. In fact, Lydia does put her family's reputation in danger through running off with Wickham and would have ruined her family forever had Darcy not come to the family's rescue. This type of improper behavior is dangerous to a society because societies are founded on certain principles and to disregard those principles can cost the security and happiness of others. Mr. Collins phrases it best when he observes after Lydia's behavior, "This false step in one daughter will be injurious to the fortunes of all the others; for who .... will connect themselves with such a family" (Ch. 48).