Warning: potentially triggering.

Well, okay, first let's review some statistics. At least one in six women will be raped over the course of their lives; actually the numbers I see are usually significantly higher than this (rape statistics suffer due to extreme under-reporting). Moreover, about half the time it will happen (the first time) before they turn eighteen. Lastly, about two thirds of rapes are committed by friends and acquaintances of the victims.

So, if you take an adult woman at random from your community, there is a significant chance (again, the numbers on the site I linked to are abnormally low, but they give some idea) that she has already been raped or sexually assaulted by someone she knew, and is therefore very aware of this danger; even if she hasn't been raped, she has most likely been taught at a young age to fear rape and to take appropriate precautions (you'd think we'd start teaching men not to rape, but no, it's apparently up to women to stop this from happening to them).

So what does this have to do with objectification? Well, look at what happens on the relatively rare occasions that rapes lead to criminal trials: the woman is interrogated about what she was wearing when it happened, whether or not she fought back (because if she was too scared to move, it must have been consenting), why she was out drinking/walking/dancing, whether they acted in a friendly manner toward the attacker. In the overwhelming majority of cases, the victim is emotionally brutalized for the duration of the trial, and then the rapist never spends a day in jail. Through it all, the implicit message is clear: the only reason women might demonstrate comfort in their own bodies is if they're looking to attract men, and indeed this is their sole purpose, and if they happened to actually "get" a man during that time, they should feel grateful and not niggle over little details like consent.

So, confronted by people who take this objectifying attitude toward women, your average female - who might have already been raped at some point in her life, and is certainly aware of the possibility - is likely to get a little upset, and rightly so. If she feels like you're basically a decent group of men who might just be a little misguided, she might give you the benefit of the doubt and speak out, hoping you will listen. More likely, though - if she's not yet comfortable with the group, or if her voice has been repeatedly ignored - she will remain silent, and take leave of the group at the earliest available opportunity. The risk is not just to her social status but to her body, her sexuality and her dignity.

(I am infuriated by the suggestion that offense is precisely and only a form of status-seeking behaviour. Some white, heterosexual males might perhaps display their progressive values for the sake of signaling social status; but for visible minorities, there is quite a lot more at stake.)

This is not the only reason to avoid objectification, but it is certainly sufficient and compelling enough on its own, I think.