Despite the achievements made for women in the 1920's, such as the right to vote, how was this era detrimental to the image and development of women?
A hint to the answer is given in your keyword tags. It is possible to argue that women in this time period came to be seen as sex objects in a way that had not previously been true.
This argument is a fundamentally conservative one. It rests on the idea that women in the '20s started to act and dress in ways that made them less respectable in the eyes of men. The flappers would be a major part of this argument. They dressed in much more revealing clothes, wore more cosmetics, and were more willing to engage in at least some degree of sexual activity outside of marriage. If you are so inclined, you can argue that this led to a decline in respect for women.