I think the truly important question is: Are those differences caused biology or society?
Or to phrase the question in a different way. If risk behavior is a socially learned behavior, and risk behavior is the cause of gender imbalance in SV entrepreneurs, what would the ethical action be to create equal opportunity for people of both genders?
Let's ask the question another way: if schools (and parents) are currently educating boys to take more risk (or educating girls to take less risk), should they start treating both sexes the same way?
What schools could do is educate about actually risks, so that any personal or cultural level of risk aversion is confronted with reality. That would be treating children of both genders equally and could mitigate differences between genders.
Those biases are subtextual, but very powerful. There's a nice recent article demonstrating some of them: http://www.slate.com/articles/technology/bitwise/2014/12/wom...
Risk tolerance leads boys and some girls to take stupid risks from adolescence to? Well, for boys, over-representation in correctional institutions.
If one could just get all to avoid stupid risks but take other more acceptable risks, I suppose but can they be decoupled?
This is not to say that oppotunities should not be there for all to consider and take, if they so desire... just making risk in general more acceptable can have unintended consequences --unless there is a way to direct the risk energy into productive avenues (i.e more job risk tolerance but less risk of engaging in dangerous activities..