What is the reasoning that women must be elected to a board? 

It is difficult to make a rationale for discrimination on an outward trait that is still founded in meritocracy. 

There can be a rationale for more diversity.

Diversity is not in physical terms - but rather in ideas. If boards are comprised of "yes men" who are proxies for certain interests, as opposed to being comprised of independent thinkers who offer unique perspectives, experience, and knowledge which are relevant and enrich the quality of business decision making, this could benefit the organization, and contribute to the strength of the Enterprise.

However, such independence must still be vested in the success of the company and contribute to stability in Corporate governance.

They should look at Board nominations, supporting more open nominations, facilitate shareholder due diligence, and ensure minority shareholders can organize their votes to nominate a Board representative of all shareholders.