And yet, stereotypes do play a role in generating prejudice. In a utopic unprejudiced society, where all people are treated exactly the same by everyone and where there's no pre-conceived notion of "gendered careers", then each person would stand for themselves and their choice of career wouldn't be affected by externalities.

As is, this is 2017 and we have white supremacists chanting about Jews and ramming cars into people. Clearly, we are not even close to that Utopia.

But besides that, if the solution is to dedicate any special effort in hiring from this or that group, then employees from that group will feel they have to prove they really are at the same level as the others. Which is the opposite of what you wanted, and exactly what the female engineers in this interview complain about.