Conservatives outright reject the idea that big-government gun-control schemes would reduce mass shootings like the recent murders committed at a Planned Parenthood clinic in Colorado Springs. So why do so many conservatives seem to believe a big-government mental-health-care scheme, like the bill sponsored by psychologist and congressman Tim Murphy (R-PA), would be any more effective?

Murphy's bill would reorganize and expand the federal government's involvement in mental-health care. It would create a new Assistant Secretary for Mental Health and Substance Use Disorders at the U.S. Department of Health and Human Services. It would create an Interagency Serious Mental Illness Coordinating Committee. It would encourage telepsychiatry--by subsidizing it. It would expand Medicare and Medicaid subsidies for mental-health goods and services. It would leverage federal grants to coerce control how states treat mental-health patients suspected of being a threat to others. It would do other things.

Conservatives have lauded the bill and demonized its opponents. In October, National Review editorialized basically that Murphy's bill would manage mental-health treatment from Washington better than Washington has ever managed mental-health treatment before.  Last week, The Wall Street Journal editorialized that opponents, including some Republicans, "object to involuntary commitment for the mentally ill, despite overwhelming evidence of the risks to society and the sick." The Journal neglected either to recognize that involuntary commitment is a dangerous power for the government to wield, one with both benefits and costs, or to offer evidence that the benefits to society and the sick of broader involuntary commitment would exceed those costs.

The best way for government to aid the mentally ill is not a medical question. It is an economic one. What makes conservatives think that command-and-control economics will work better in mental health than in any other area? (Or are they just looking for a talking point in response to mass shootings?)

But that's not what I'm here to tell you about. I'm here to talk about a Balanced Budget Amendment.

The Congressional Budget Office projects the Murphy bill would increase federal spending by a mere $3 billion over 10 years. But that projection comes with a very big asterisk.

The bill contains a weird quirk. It allows, and creates the expectation of, broader federal subsidies for mental-health services under both Medicare and Medicaid (much of it for ObamaCare's new Medicaid-expansion population). But that broader coverage can happen if and only if the chief actuary of the Centers for Medicare and Medicaid Services certifies that such additional coverage will not increase net Medicare or Medicaid spending. The idea being, presumably, that this coverage expansion will be budget-neutral because the feds will pay for that additional stuff (much of which is currently being paid for by states) if and only if it produces, or CMS can otherwise find, offsetting savings elsewhere in Medicare and Medicaid. Without that funny little requirement, CBO projects the Murphy bill would increase net federal spending by as much as $66 billion over 10 years.

In other words, if those required certifications can be gamed--and political pressure from states and mental-health-care providers to game it will be considerable--the Murphy bill would increase federal spending by as much as 22 times the official projections. That's not just an asterisk: it's an exponent.

What does all this have to do with a Balanced Budget Amendment? It seems ideologically inconsistent for rock-ribbed, limited-government conservatives at the Wall Street Journal and National Review to support a bill like Murphy's. But in a world of deficit spending, it costs them little. 'Meh,' they can say, '$3 billion over 10 years is a drop in the bucket.' And it is easier to hand-wave away the looming threat of an additional $66 billion of federal spending.

Were there a constitutional requirement that federal spending must be financed by current taxation rather than deficit spending (i.e., a promise to raise taxes in the future), these conservatives probably would think twice about a bill like this because of the tax increases it portends.

Interestingly, both the Wall Street Journal and National Review have long editorialized against a Balanced Budget Amendment. Their principal objections are (1) to be effective, the impetus for a balanced budget must be political, not constitutional, and (2) a constitutional amendment would be difficult to enforce and, therefore, easy for politicians to game.

What these objections fail to appreciate is that the very process of ratifying a Balanced Budget Amendment would alter the political landscape, by creating expectations and thus a political constraint that augments the constitutional constraint and helps to make that constraint binding.

No Balanced Budget Amendment would or could be flawless. It would just be a vast improvement over what we have right now. Consider: following that ratification process, the politics of government spending might be sufficiently altered such that, when politicians presented conservatives with (say) a new big-government mental-health bill, conservatives would be forced to think about the additional taxes required to fund it, and would, therefore, reject it out of hand.