Co-blogger Scott Sumner argues for, without quite endorsing, Senator Mitt Romney’s proposal for a large child allowance. I won’t lay out the specifics of Romney’s proposal in detail because Scott has already done it and the Tax Foundation has provided even more details.

I will point out that the budget cost of the plan, all else equal, is estimated to be about $229.5 billion annually. While that might not sound like a lot in this time of trillion-dollar spending programs, it is a lot.

Of course, not all else is equal. If Romney got his way, the child care tax credit would be eliminated, which would save $117 billion annually, leaving $112.5 billion as the net cost. He would also reform the Earned Income Tax Credit, saving $46.5 billion annually, driving the net expenditure for his plan down to $66 billion.

He would come up with the $66 billion by increasing taxes in three ways and cutting two other spending programs.

While the Tax Foundation did an excellent job of analyzing the provisions of the Romney plan, it did make one error. The analysts, Erica York and Garrett Watson, state:

Romney estimates eliminating the SALT deduction would result in $25.2 billion in annual savings through 2025.

But eliminating the SALT deduction doesn’t save money: it costs money. It costs taxpayers who will lose the deduction. Of course, York and Watson may be quoting Romney and so it may be Romney’s mistake. But it is a mistake.

Note also that the child allowance starts phasing out for single taxpayers with income about $200,000 and for married, filing jointly taxpayers with income above $400,000, at a rate of $50 per $1,000 in income. That implies that very high-income people, virtually all of whom are already in a fairly high federal tax bracket, will see their marginal tax rates increase by 5 percentage points. That’s if they have 1 child. And if they have 2 children, their marginal tax rates will be 5 percentage points higher over an even larger range of income than the Tax Foundation’s graph shows.

Most of these high-income people will be in a 35 percent tax bracket. This phase-out increases their marginal tax rate by 14.3 percent (5 is 14.3 percent of 35). The efficiency loss, also called deadweight loss (DWL), from taxes is proportional to the square of the tax rate. So the 14.3 percent increase in the marginal tax rate doesn’t increase DWL by 14.3 percent. It increases it by 30.6 percent. (Take 0.4 squared divided by 0.35 squared and you get 1.306.) That’s a large increase.

And why all this? Why does it make sense to subsidize people having children?

Two other points.

First, although Scott Sumner says that the proposal will increase equity, he doesn’t define equity. But implicit in his discussion is the idea that equity is synonymous with income equality or, at least, reduced income inequality. That’s not my view. My view is that people are treated equitably when other people don’t take their stuff. Romney would tax people more when they live in high-tax states and thus lose their deduction of state and local taxes. That’s not fair. (I think, along with Scott, that the SALT deduction should be zero, but in return, marginal tax rates for high-income people should be cut.)

Second, what happened to Romney’s fear, which he once had, of the deficit. The budget deficit is huge this year and, although it will likely be lower next year, it is set to be at least $1 trillion annually for a long, long time. We should be looking at paring down “entitlements” such as Social Security, Medicare, and Medicaid, not adding new ones.