President Obama focused on budget and economic issues in his press conference last night. One concern raised by reporters was that federal deficits were exploding and that Obama’s big spending plans would seem to make the problem worse.

Obama’s response was essentially that higher spending reduces the debt problem, which would strike most people as paradoxical to say the least:

Here’s what I do know: If we don’t tackle energy, if we don’t improve our education system, if we don’t drive down the costs of health care, if we’re not making serious investments in science and technology and our infrastructure, then we won’t grow [the economy by] 2.6 percent, we won’t grow 2.2 percent. We won’t grow. And so what we’ve said is, let’s make the investments that ensure that we meet our growth targets that put us on a pathway to growth as opposed to a situation in which we’re not making those investments and we still have trillion-dollar deficits.

First note that Obama’s budget would drive government health care costs up, not down. But aside from that technicality, the economics of Obama’s theory don’t make any sense.

Government spending on infrastructure, education, science and energy are already at high levels. For example, infrastructure spending today is as high as it was during the 1950s, and higher than it has been in recent decades. If government worked efficiently—as liberals believe it does—then all the highest-valued uses of taxpayer money would already be funded. At the margin, the only place for Obama’s new spending would be on low-value items of less economic importance.

Thus, Obama’s new college subsidies might induce some added young people to attend college, but most of those people are probably pretty marginal students because the high-quality students are already going to college. The marginal students might pick up some added skills, but at the cost of higher tax burdens and less economic output in the years when those folks are out of the workforce. Liberals assume that more spending on any activity they are interested in, whether public or private, is always better, but the real goal of economic policy is to find the optimum because all spending has a cost. (And the optimum level of government spending on most things is pretty darn low, or zero, in my view).

Obama is essentially claiming that even with federal, state and local spending at about one-third of GDP, there are government spending projects left over that are so powerful that “we won’t grow” if they don’t happen.

Serious economists know that that is nonsense. Most government activities have negative effects on growth, not positive effects. Take the largest federal program, Social Security, which will consume about $660 billion in taxpayer money this year. The program is a negative on economic growth because it suppresses personal savings and the taxes to fund it create large distortions. Lots of liberal economists support such transfer programs for non-economic or “social” reasons, but few economists would argue that they expand GDP on net.