From time to time, I've written on this site about the problematic Diversity Imbalance in the software development profession, and how we need to take deliberate action to increase the proportion of underrepresented groups. This is all well and good, but naturally leads to the questions of what underrepresented groups we should be concerned about. In ThoughtWorks we've been using the term "historically-discriminated-against"  to help focus our thinking for one of the main drivers for embracing diversity. 
Humanity has a consistently sad record of pushing groups of humans down. Historically-discriminated-against groups include women pretty much everywhere, African-American and Native-Americans in the United States, lower castes in India, aboriginals in Australia, homosexuals everywhere… sadly the list is long.
Historically-discriminated-against groups are often minorities, but not always. Blacks in South Africa have always been a considerable majority, but are historically-discriminated-against. Often historically-discriminated-against people are visibly different, based on race or gender. But they can equally well not be as visible, such as religious groups or homosexuals.
The historic discrimination is the essence of why we should work to support fixing problems. One might argue that the under-representation of men in nursing is as problematic a diversity imbalance as that of women in tech. While I don't see a lack of male nurses as a good thing, I think it's less of a concern because men have not suffered the historic discrimination that women have. Similarly if someone discovered that green-eyed people were disproportionately rare in the software industry, again my concern would be less because of the lack of historic discrimination. (Although I would still find such a disproportion intriguing.)
There's an important point about the "historical" in this definition. Many historically-discriminated-against groups have legal and social protections from discrimination these days. In America it's now socially unacceptable to make public racist or sexist comments, and illegal to carry out most forms of racist or sexist discrimination. But you can't cure centuries of historic wrongs in just a few years. This is the fallacy of people who advocate for gender-blind and race-blind policies. It takes many generations to undo the effect of centuries of discrimination, so just because the law and society are beginning to catch up doesn't mean the work of supporting historically-discriminated-against groups can stop.
So when we see only 27% of software developers are women in a world of 50% women, the fact that women are historically discriminated against is evidence that the effects of their historical oppression haven't yet been corrected. While some may argue that there's a biological explanation for the lack of women programmers, I consider that to be a treacherous argument. There's no evidence to support that women are less capable programmers (other than the circular one of their lack of numbers). Worse still, such biological and cultural arguments have a long history of being used to justify discrimination. So unless credible evidence appears, I think it's wise to consider that an underrepresentation of a historically-discriminated-against group is a sign that we haven't yet finished the task of correcting a long-running wrong. And until we do, our vision of a meritocratic profession will be undermined by the reality of the imbalance.
1: The precise term was coined by Bill Kimmel inspired by one of our values statements of Social Responsibility: "We strive to redress historic discrimination, including that of race, gender and sexual orientation.". Similar phrases appear in various parts of the world, but this is the origin of our usage.
2: There are many aspects to diversity, which is why "diversity" is such a tricky word to work with. I often see articles extolling the benefits of diverse teams, where this diversity is looking for diversity of thought. This is valuable but different from a focus on the historically-discriminated-against. Fortunately these various aspects of diversity usually go together..