Commentators are already implying Democrat Elizabeth Warren’s new universal child-care plan will be “good for the economy.”

Moody’s Analytics reckons subsidies will induce more mothers into the labor market, raising growth rates by 0.08 percent per year over a decade. Others say that cheaper out-of-pocket child-care will reduce time spent out of the labor force by working mothers, and this greater maternal labor market attachment will boost recorded productivity and women’s earning potential. Combined, it is said the universal program will raise the economy’s productive capacity and thus recorded level of GDP.

Such claims about heightened measured economic activity are not crazy. But previous research for England has found that the effects are unlikely to be as great as proponents imagine.

The roll-out of free child-care for three-year-olds there induced 12,000 extra mothers into work (coming at an extremely high cost of around $84,900 per job). This suggests government subsidies resulted in substantial crowd out of other informal or paid care, meaning overall the substitution effects (the higher effective wage inducing more labor supply) only narrowly exceeded the income effects (the higher effective wage reducing labor supply as people took more leisure with their child-care cost savings). Along the way, there was substantial “deadweight” — subsidies going to people who would work or stay attached to the labor market anyway.

But let’s suppose the proponents of Warren’s scheme are correct about their estimates of bigger effects here. Does any boost to measured GDP mean child-care subsidies are “good for the economy”? The answer is “probably not.”

GDP should not be confused with general economic welfare. Economists generally start from the view that free action in the economic sphere — people acting on their own preferences — maximizes economic welfare except in cases when there are market failures present. It is not clear what markets failures exist in relation to female labor force participation and child-care. That means subsidies to make child-care free, or nearly free, mask the opportunity cost to the parent of putting their kids in daycare in a way that harms broader economic welfare.

The idea that non-attachment to the labor market is a market failure needing correction is particularly peculiar.

Every day we freely opt not to maximize time at work or our productivity. These are choices that come with a significant opportunity cost, not least of time, after all. Some men and women obtain more “utility” from dedicating themselves to family life. Others may decide to work in vocational jobs, or part-time, or on activities that give them substantial non-pecuniary satisfaction, even if this does not maximize their productivity or wages. Some people decide not to invest in their own human capital to boost their earnings potential; others to care for an elderly relative nearing their end of life.

Why should government act to incentivize greater parental attachment to the labor market through child-care subsidies but not, say, incentivize French teachers to train to work on Wall Street or as engineers?

If failing to reach your labor market potential is a cause for intervention, then what about subsidies to other groups, such able-bodied retirees or non-working partners in single parent households with no children?

If child-care costs are too high to allow parents to be as productive as possible, then what about out-of-pocket housing, transport or training costs that prevent other people from working where they would be most productive?

Once you think about it, the idea that the role of government is to maximize labor force attachment and recorded productivity is bizarre – with huge implications that justify a whole host of new interventions.

And that would only be looking at one part of the equation too. Large new subsidies would ultimately have to be financed by raising taxes, as Warren acknowledges. Raising them on incomes for some would reduce their return to work and so labor force participation and human capital investment. Raising them on wealth, as Warren suggests, will reduce the return to saving and investment – which could reduce productivity. It is not clear what the net effect of this would be overall.

So is there ever a case for child-care subsidies under a “neutral” framework that allows preferences to be realized? Perhaps.

In some cases, the provision of means-tested welfare benefits without work requirements may reduce the incentive for parents to work. Targeted assistance to rebalance this disincentive may be desirable for those on low incomes, and indeed already exists in the form of the earned income tax credit.

More broadly though, if governments want to act neutrally in relation to children they should either operate no subsidies at all or else support families with children through tax allowances or distributions available to all children.

That way, parents get to decide what is best for their child without warping the financial incentives and structure of the child-care sector itself.