This question was brought to the front of my attention by a recent essay in The American Prospect. Monica Potts responds to Paul Ryan's philosophy of government:

The conservative approach to government stems from a basic tenet of free-market economics: that people always act rationally to maximize their own benefits, and that from this rises a general state of well-being for society as a whole. But this isnt always true. One of the hottest academic disciplines to arise in the last few decades is behavioral economics, which explores the ways in which people behave irrationally. In addition, easy-predictable problems with certain markets prevent us from achieving the best outcomes. These two facts have consequences for how we should think about government in certain instances. There are many ways in which the government can make better decisions with our money than we can, and there are many ways that the Ryan budget would make society worse off by getting rid of government programs.

She goes on to explain her top-five list, which you'll have to go there to read. But I would add one more thing big government is good for. And to my mind, it is the clearest and most pressing one of all. But first, back to college for a minute.

It is a testament to my undergraduate professor of Political Theory, John Roos (now emeritus) that I remember the contents of the final exam I wrote for him. Of course, the main reason I remember it is that I had overslept and missed the exam I was supposed to take. So the professor had to improvise with my exam. He sat me in his office, clearly flustered that I had overslept, but pondering what would be merciful and fair in my situation.

He handed me a blue book and said, "OK, there's been a coup and another of the Yugoslavian states has successfully seceded. You're a famous professor of political theory and they bring you in to help them construct their new government. What do you tell them? You have three hours. My grad student will sit here while you write." (The grad student was not pleased with this decision.)

I wrote that the primary principle of government is to preserve as much individual liberty as possible, while still actively promoting a common set of public goods. In theory, everyone wants minimal government. The debates are about what counts as minimal.

With Mitt Romney's selection of Paul Ryan, we have a faint chance for this debate to happen over the next two months. Most of us have grown skeptical of our electorate's ability to have such a debate, but the opportunity is here in a way it hasn't been for several elections. Many of the speeches at the Republican National Convention, such as Gov. Chris Christie's last night, will focus on individual liberty vs. big government (or "coddling" government, as he termed it last night).

When I think back on my exam answer, I know most of it was boilerplate stuff -- not A material. The government should provide some military, roads, sanitation, police, fire departments, primary and secondary education, and so on, I wrote. My government for hypothetical Slavinostia looked a lot like a center-right American administration. I was tired, not remembering the finer points of Rousseau, and fell back on the political theory that I knew from just living in America. Not even B material.

But there was one breakthrough moment, one which I carried forward in life and has affected all of my voting since. I ended up writing a large portion of the exam about the necessity of environmental protection at the federal level. Many environmental problems can and ought to be addressed locally, but some of them simply cannot be. I also argued then off the cuff, and now would do so with much more data and (I hope) sophistication, that individual human beings are almost universally unable to imagine or prevent our large-scale effects on the global ecosystem. We don't comprehend the scale of our effects; and we don't muster the will power to change our behavior. We have entered the "anthropocene" era of planet "Eaarth," as Bill McKibben has renamed our beleaguered planet.

Environmental regulation is uniquely positioned, then, to both promote the public good and preserve individual liberty in the long term. My center-right government, geared towards liberty, demanded a massive federal regulatory agency. In other words, to maximize liberty in the current era, even a minimal government needs a fierce EPA. In my world, Slavinostia's EPA was going to be its most important federal agency. Its bizarre government looked, in the end, like it was designed by the team of Ronald Reagan and John Muir. (Or maybe something like what David Frum espouses.)

I still agree with my undergraduate self. If I had to pick one thing that big government is good for -- and one which I wish were a larger part of the current debates -- it is environmental protection.