I'll take the first run at that.
It's becoming increasingly well documented that using the individual as the basic measure of tax liability and the basic unit for giving tax credits or tax cuts of any kind is very important to the status of women. Detailed studies have been carried out in the OECD showing that as any form of income splitting, joint filing, or joint taxation measures has been eliminated, women's overall economic equality has increased. Women's participation rates in paid work have increased. Women's access to child care resources, etc., has increased. It's absolutely, scientifically been proven conclusively. From a substantive perspective in this day and age, to turn around and start trying to hand out benefits to the family really ends up being a shorthand way of saying that we're trying to put men back in the financial driver's seat.
As illustrated by the numbers generated by the pension income-splitting provision that was put into place a couple of years ago, the higher the income a single-income earner has, the greater the tax benefit from pension income splitting; the greater the tax benefit to income splitting, the greater the disincentive to women's economic autonomy. It then becomes a family liability for a woman to have an income. It becomes a family liability for a woman to have money to put into a tax-free savings account. This inferentially reinforces a pattern that is dysfunctional.