Feminist here and I completely agree that men and women are not biologically identical/equal, that is just stupid. That does not mean we cannot be equal though. Men and women both have their own biological strengths and weaknesses. The way I see it is that you're more likely to see a man in a hands on, labour type of work. However, you're more likely to see women in more nurturing type jobs, such as nursing. But our biology does not define us, and we should not ridicule men and women that want to do things that are typically associated with their gender. It is about shattering these gender stereotypes. The biology of our body seems to be an indictor to how we're likely to act, and define what we enjoy, but we all know there anomalies, and many men and women (if not most) possess some qualities that may be typical in the other gender.
Referring to the 'man up' phrase, it is not the worst thing in the world, but it does make me cringe when someone says it. Not only is it sexist to women, but is sexist to men.