We have a pernicious, systemic problem in what we call the software industry. We are excluding people from participating on the basis of superficial differences, especially gender. The wages of this collective stupidity are reduced productivity (and therefore prosperity) and a more impoverished community lacking in the kind of diversity that makes human societies worth living in.
There are many important reasons why we must create this improved environment, but two that especially stand out to me. Firstly, there's the moral imperative; that equal consideration of interests is just the right thing to do. We don't really need any more justification than this to proceed confidently towards the goal of creating a better community.
First, let's remove a common source of confusion. By equality I mean 'equal consideration of interests'. I don't mean pretending that everyone is the same; that's clearly untrue. For instance, we happily provide urinals for biological males because of anatomical differences in the sexes, but that doesn't mean we're neglecting the interests of biological women in doing so. To argue otherwise is to confuse similarity and equality (in much the same way that an uneducated person may confuse the uncertainty principle with the observer effect).
So that form of opposition to equality is nonsense, and to use it is to invite embarrassing rhetorical defeat. In the case of women in tech, equal consideration of interests means that today we have to actively do more for women because the environment is currently hostile to them at every level. Doing nothing does not create a 'level playing field', a meritocracy, or any other wonderful ideal. We need to actively push back and explicitly create diversity in tech. If you think that itself is injustice, think harder.
There's another, nastier variation on this argument, insinuating that action is only necessary because women lack the innate ability to succeed alone. It's an argument that's so weak it is hardly ever directly vocalised, but it's a widely held belief made apparent by complaints about the danger of using 'positive discrimination' or 'affirmative action' to bring about change. I almost feel pity for those trying to use this argument, but that won't prevent me from destroying it.
Men and women are not opposites. If men are from Mars, women are from Mars. Even if you compare them as two populations and not individually, the physical differences are small and the intellectual differences don't exist. The reason for this is that in reality, human sexual dimorphism just isn't that large. Go look it up. Then deal with it.
Note that even if this was not the case, it still wouldn't be an argument against the equal consideration of interests. I'm just refuting it because it's a fallacy; if you follow this line of reasoning you can't win, you can only lose.
So if you're truly looking for the reasons why there is a huge gender imbalance in software development, look elsewhere. A woman programmer is just as able as a man. Differences in capability cannot explain why by some estimates only 1.5% of contributors to open source software are women. An openly hostile environment that nobody should be subjected to can explain that difference.
So having put the fallacies opposing equality to bed, let's consider the second pillar of our reasoning; the economic argument. As an industry (and as a society) we're far poorer when we arbitrarily exclude people from contributing. We are living in a period where demand for experts in the field of high technology far outstrips supply and will continue to do so for the foreseeable future. This means that there's no need for intelligent developers to fear new entrants to the market, in fact our future depends on them. Sadly, many who could contribute their talents to our collective endeavour are unable to do so, because they're missing from our community. They either left, never felt able to join, or contribute less as a result of the environment we've created.
Well, it's time to uncreate that environment. To reform the landscape is going to take time. It will also require us to use every weapon in our arsenal, from the precise to the blunt, the inoffensive to the blasphemous. That will include things like 50% women speaker lineups at conferences, a zero tolerance to bullying & harassment with strong legal enforcement, and high profile all-women teams to counter the current men-only cabals. Not all of the weapons will be compatible with our current illegitimate notion of meritocracy. That is by design.
If you believe in real equality, then it's time for us to fight. It's a war that we can win.