Makes sense for the employee, but not for the employer; for the same reason that having a football team made up entirely of quarterbacks is a bad idea. A diversity of hiring (not just gender, but age, experience, background, and yes, skin colour) makes for a more diverse team that understands a much larger potential target market. It also has a much broader base of experiences to draw from during planning and decision making. All of this ultimately results in better software and better products.

Not even remotely true. The diversity of viewpoints exposed by hiring as broad a variety of people as possible make for better decision making, better analysis, and ultimate better software.

Ok, I'll bite. Having a decent variety of people of all heights (from very very tall to quite short) on a team would certainly allow you to design a better shelving system — the diversity of viewpoints allows for a much broader basis for design and accessibility. In this case "viewpoint" is even used literally: when you're 6'3", the top of the fridge is a shelf, and when you're 5'2", the top of the fridge is invisible.

More industry diversity is good, period.

Well, I personally think that the people controlling the jar have good business sense, and that gender parity in the IT industry is a good thing. That's probably true on a number of axes: the IT industry is too male, too pale, and too immature.

But whether you agree with that statement or not, I'm pretty sure that we can agree that they didn't set out to encourage more guys to take computer science courses and bungle it really badly.

No it doesn't — it presupposes that a 50/50 distribution is the desired goal of whoever is manipulating the jar of marbles. I think it's pretty clear that gender parity is in fact what the people making the incentive want.

If you don't think that is valid, just, or reasonable, you're free not to. You should argue that point with the people funding the incentive. Money is speech, so they're well within their first amendment rights, but maybe you could convince them.

Of course, you haven't provided any arguments at all why a 50/50 distribution of men and woman in the industry isn't a desired goal...

And also, there's the tiny problem that saying "having as many women as men in the IT industry isn't valid, just, or reasonable" does makes you sound like a bit of a dick.

No, seriously, why would anyone do anything else if the goal is gender parity in the industry?

Let's take gender out of the equation. Say you have a jar full of ten million marbles. 95% are green, 5% are yellow. 10000 marbles are added to the jar every year. Your goal is to make the jar 50% green, 50% yellow, and you can't take any marbles out of the jar. Changing the distribution of marbles added each year to 50/50 will never make the entire jar 50/50. The only way to solve the problem without removing existing marbles from the jar is to raise the distribution of marbles added to more than 50% yellow. Clearly the most effective solution problem is to only add yellow marbles to the jar at all.

Back in the real world: you either need to fire men who don't deserve it, hire equal numbers of men and women and wait a generation or two for enough people to retire, or try to hire more women than men. Because math.