For the greater part of the twentieth century, mainstream economists viewed negative (technological) externalities as a prima facie justification for government intervention in the market. Absent such government action, they argued, nothing would be done to prevent or remedy the damages third parties suffered as a result of unrestrained “spillovers” or “neighborhood effects.” For example, in the words of Joseph E. Stiglitz, “without government intervention there would be an underprovision of pollution control” (1988, 76). Even such staunch defenders of the market as Milton Friedman (1962, 30) and F. A. Hayek (1979, 43–45) conceded that spillovers might justify government intervention, although they embraced neither the “blackboard economics” conclusion that government intervention is desirable and effective in all cases of spillovers nor the “nirvana” standard implicit in Stiglitz’s use of the neoclassical welfare-economics term underprovision.