Of course a woman can decide to wear a bra or not, but she needs to live with the consequences.
In this case, the disapproval of her mother, and the discomfort of the boyfriend, and maybe the mother.
Also, many women, especially if they are large breasted, look very sloppy, unkempt and inappropriate if they are not wearing a bra.
Not a big deal when in the comfort of your own home. Or if you don't care how you appear in public.
Even a well built woman, or one small breasted, doesn't exactly look public ready when just wearing some tshirt, sweater or shirt.
There is of course, if the woman has a good figure, the risk of looking without intention overly sexy and attention getting.
Breasts are obviously nothing to be ashamed of. I for one am not advocating the wearing of bras to cover themselves up because of prudishness, etc.
Overall, it's just not really an attractive look beyond the occassional males "ooga ooga, wow look at those" looks
There's a very very brief period of time in a womans life where she can really get away with no bra in public, and that's if she has a good figure.
Overwise, if she has big breasts, they just look like big udders slopping around (which is by the way really uncomfortable), or small or medium size udders shifting around.
Sturgis, if I'm not mistaken, you're not one of the traditional womens breast lovers club, so you may be coming at it from a different perspective.
So if you're a woman who doesn't want to wear a bra in public, go ahead. But you won't look the way you think you do in your mind.