Ooops - pressed post too soon - I absolutely agree that it is wrong for anyone to feel that they have to wear a bra, in order to conform with society, when it does nothing for them personally (either by offering practical support or being something pretty with which they enjoy wearing). I don't go round looking for women who aren't wearing a bra and judging them, and I would hope that most other people don't either.
I do think that sometimes people put pressure on themselves, and judge themselves far more harshly than the world actually does. For example, I didn't manage to successfully breastfeed my dses past 2 or 3 months, and I felt a total failure for this. Most of my friends breastfed with no problems (or no problems apparent to me, at least), and I compared myself to them and judged myself very harshly - which contributed to PND.
I do wonder whether this is, in part at least, a similar issue. Whether women have taken on board the belief that they must wear a bra, and so, like you, they do so, even though it makes them uncomfortable or resentful, but actually the vast majority of society wouldn't even notice if they didn't wear a bra, or wouldn't care that much either way. Of course, the question of why women feel they need to wear a bra is a much deeper one, and one I am not qualified to examine - though I deplore it.