Unless we know and are actively mindful of the common biases that negatively affect women, we’ll almost assuredly reinforce them. Even wonderful people with good intentions fall prey to bias. Unconscious bias rears its head in so many subtle ways. Unless all these guys are aware of all of the major patterns of biases, can identify them in their own actions, and see how how those biases play out institutionally, then there's still a lot of work to be done here.
For example, take stretch assignments. Managers may tend to give stretch and difficult assignments to men over women simply due to the unconscious way we’re affected by stereotypes, and these stretch assignments are often the key to career advancement. Or take social networks. Imagine a situation in which a boss always plays basketball with his male colleagues after work. This can end up creating a situation in which most women (and non-athletic men) are excluded from important social contact, work-related information, and access to power. These dynamics aren’t obvious, but they are powerful, and it takes concerted effort to both learn common blindspots and be vigilant to not fall prey to them.