Why are some readers upset by Jane Austen's treatment of Mary Crawford?

A case of building expectations and readers' complicity:

Normblog had a post about one of Jane Austen's more controversial female characters. He quotes another Austenite scolding Jane for being too harsh with Mary Crawford, of Mansfield Park.

Old Fogey ....[i]s taking the author to task for her treatment - or, as he sees it, mistreatment - of Mary Crawford in Mansfield Park. He loves Mary Crawford as he loves Jane Austen, and reckons Mary gets a shabby deal from her creator....

I wonder if there really is an orthodoxy about this. Apart from several Austen biographies, I haven't read much of the critical literature about her, but what I have read gave me the impression (registered here) that the Old Fogey's view has been shared by quite a few of Jane Austen's...

I'm familiar with Old Fogey's attitude. Many a-reader have castigated Austen for exposing Mary's calculating nature at the end of the novel, as if it were unmerited. This streak in Mary is well-concealed throughout the novel, though not undetectable to the scrupulous reader. I also have my own theory that Mary is unambiguously appealing to men, who are built by nature to turn a blind eye to a woman's less ethical aspects, as long as her looks are sexy, her mind intelligent and her behaviour flirtatious...

I think Jane Austen was playing her usual ironic games with her readers, testing their attention to the details she provides and how far their voluntary complicity in the willful blindness of some of the characters.

It is true that many Austen readers have fallen for Mary Crawford's enthralling charisma. Early in the novel, she is observed as being kind and sympathetic to Fanny, when she displays an acute awareness of Fanny's lowly and insecure status in her uncle's household. The reader who has been an observer of Fanny's cruel abuse and emotional neglect at the hands of her "benefactors", is relieved when such a fashionable, socially-confident and desirable quest displays decency and sympathy for Fanny's choices and tries to help fend off the attacks from her odious aunt and cousins. As readers, we are grateful for her intervention on behalf of Fanny. Perhaps we feel she is Jane Austen's messenger in the novel, sent to guard and nurture the emotionally starved, warmth deprived Fanny. Like everyone else in the novel, even Edmund, we become infatuated with her. The only one who resists is Fanny, in spite of being the object of Mary's affections and good ministrations.

I think we are meant to fall in love with Mary, and secretly chide Fanny for keeping a corner of cool scepticism about her. We suspect it is due to sexual jealousy. When Fanny’s superior judgment and perspicacity are confirmed, we feel slightly mortified at having doubted her, for having been impatient with what we take to be her excessive Puritanism.

The reader's epiphany comes at this moment, which Edmund recounts, reluctantly, to Fanny, towards the very end of the novel:

“She spoke of you with high praise and warm affection; yet, even here, there was alloy, a dash of evil—for in the midst of it she could exclaim 'Why, would not she have him? It is all her fault. Simple girl!—I shall never forgive her. Had she accepted him as she ought, they might now have been on the point of marriage, and Henry would have been too happy and too busy to want any other object. He would have taken no pains to be on terms with Mrs. Rushworth again. It would have all ended in a regular standing flirtation, in yearly meetings at Sotherton and Everingham.' Could you have believed it possible?—But the charm is broken. My eyes are opened."

These words should act upon us as a rude awakening from our fond infatuation with her. When all is said and done, it is not her brother or Maria who are to bear the ultimate burden of responsibility for their disastrous choices but Fanny, for having made the choice not to marry Crawford. Fanny, who had fully figured out, when none other did - that Henry's moral weakness far outweighed any benefits she might gain from an alliance with him- is accused of not doing what is expected of a girl in her position: "Had she accepted him as she ought, "

"As she ought"!

When push came to shove, Mary’s elegant mask cracks, enough to expose her as having no higher principles than those of the Bertram sisters and Aunt Norris.

She is not the authorial messenger we were hoping for. She is just another Austenian female with questionable personal priorities and a calculating nature, like Elizabeth’s friend Charlotte Lucas, or Catherine Moreland's friend Isabella Thorpe.

Jane Austen’s treatment of Mary Crawford is “Miltonesque”. One major interpreters of Milton's "Paradise Lost" posits that Milton deliberately made Satan an irresistibly rational and charismatic character, so that the reader would experience a personal complicity in the moral fall from Paradise which is occasioned by Satan's rebellion, and the humiliation that should accrue to such an experience.