ECO_ What is the appropriate balance between private and public

What is the appropriate balance between private and public (i.e., government) activity? Think of a case where the government has intervened (or it was suggested that government intervene) in a previously private market (e.g. Chrysler, tariffs on Japanese luxury cars, the airline industry, etc). What other examples can you think of? Using a marginal benefit/marginal cost analysis, support or argue against the intervention.