You men are not being told to be ashamed of a part of your body.  You're not being judged as being flamboyant, provocative, or slovenly if you're not all bound up so no one can see your true shape or if your nipples get hard.  Hard nipples, btw, are the bane of some women's existence.  Some women actually buy padded bras, NOT for the breast size-enhancing qualities, but as armor against viewable nipplage.  Women have a reputation for getting chillier than men, but has it ever occurred to you that maybe raising the heat at the office or wearing a sweater is a preventive measure?  NO ONE wants to hear 'headlight' jokes at work.

I'd wager that there will be just as much backtalk and frowning when a man is, say, giving a presentation while there is an erection clearly outlined in his trousers. While everyone should know that erections can be involuntarily.

To the contrary of what you write, I find a comparison between wearing a compulsory bra and a compulsory tie rather apt. They're both contraption garments, and, a tie even more than a bra, serve no greater purpose other than a symbolic status.

I've aspired most of my life to prevent wearing a tie at my work - and so far, this is going well.