Let's say you wanted to be a teacher, a field that is largely female-dominated, and all of the teachers you've ever worked with spent a large amount of their time "expressing pride in their womanhood". Let's say it's pretty hard to find another male (maybe there are one or two in the school where you work out of say 30 teachers). Would you feel comfortable with the fact that you were exposed to things that were exclusionary to men? If teaching materials were named "sis-guides" as some sort of weird pun on something? If day-to-day, you were being constantly and actively reminded that being a woman in this profession is the norm and that you are not normal?
Maybe you can look at this and say that you'd be fine with such an environment. I think most people would be uncomfortable. It's not about suppressing expression of masculinity (although what does masculinity mean anymore), it's about keeping that expression from being the only expression that gets to occur in the entire industry. Maybe we can be "proud of our manhood", but maybe tone it down a little to include women?