But if the women choose to be in the ad and they get paid, what's the problem?

Sexually objectifying portrayals of women in advertising and popular culture can have negative consequences for ALL women in society. 

Media and Sexualization: State of Empirical Research, 1995–2015

"Sexually objectifying portrayals of women are a frequent occurrence in mainstream media, raising questions about the potential impact of exposure to this content on others’ impressions of women and on women’s views of themselves. The findings provided consistent evidence that both laboratory exposure and regular, everyday exposure to this content are directly associated with a range of consequences, including higher levels of body dissatisfaction, greater self-objectification, greater support of sexist beliefs and of adversarial sexual beliefs, and greater tolerance of sexual violence toward women. Moreover, experimental exposure to this content leads both women and men to have a diminished view of women’s competence, morality, and humanity."

The goal of this review was to synthesize empirical investigations testing effects of media sexualization. The focus was on research published in peer-reviewed, English-language journals between 1995 and 2015. A total of 109 publications that contained 135 studies were reviewed.

See the review for more information.