Privtization is not a good thing for public goods. To familarize those unfamiliar with public goods:
http://www.economist.com/research/economics/alphabetic.cfm?letter=P#publicgoods
Essentially, the definition of a public good is one that would not be provided efficiently, or at all, by the private market. Roads are probably the best example, there is a reason that almost every road is publicly owned, its because a private company could never make any money off of building or maintaining a road, so they don't.
Other examples where privitization is a bad idea is where there are regional monopolies, such as a water utility company. The water company has no competitors, so like a movie theatre selling popcorn they can charge you whatever they want to maximize their profits. The government has to step in and either own such a utility or decide for a private water company what prices they are allowed to charge, effectively eliminating any advantages the private market has over the public sector.
