Art Carden and I have the monthly feature at Econlib: "Is Market Failure a Sufficient Condition for Government Intervention?" We think it's a useful and accessible primer on why pointing out various forms of so-called "market failure" (e.g. negative externalities, public goods, etc.) are not an ipso facto argument for government intervention. It's also a good introduction to some basic public choice and comparative political economy ideas.
Understanding "market failure" and the omnipresence of negative externalities can lead us to make the comparison that does matter. Implicit in negative-externality arguments for intervention is the claim that the political process will actually do what economists say it should do. That is, politicians will impose the blackboard solution. However, the public choice5 revolution that began in the 1960s has challenged that assumption by showing how governments also fail. Politicians' self-interest, combined with the limits to their knowledge, mean that they likely will not and cannot produce the ideal outcome. We are left to ponder which of two imperfect systems will serve us better: the "failed" market or the "failed" political process. We have many reasons to think that markets will outperform government in this regard, even in less-than-perfect conditions. One approach sees every "market failure" as an opportunity for entrepreneurs to solve a problem and discover, through profit and loss, how well they have done. Political processes do not have the requisite incentives and knowledge-conveying processes to do as well.This might be very useful in the undergraduate classroom.