It would appear as if she sees them as very true to their faith, simplistic, and narrow-minded. This is especially true of Mrs. Hopewell and Mrs. Freeman. However, Joy, or Hulga, as she prefers, is the opposite. She is a very strong character and a staunch athiest. As such, she rejects the simplistic, fundamentalist faith espoused by the other women in the story.
While Mrs. Hopewell and Mrs. Freeman fail to see through Manly Pointer, who presents himself as "good country people", and a simple traveling Bible salesman, Hulga does not appear to accept him as clever at first. She feels he is lacking intellectually, but that he is basically benign, and agrees to go out with him.
Hulga may be presented as a strong woman with dissident views, especially about religion and the meaning of life, but she is allowed to be made a fool in the end. When Manly convinces her to remove her false leg and runs away with it, he leaves her both literally and figuratively without a leg to stand on, a common Southern cliche with which O'Connor was undoubtedly familiar.