Perfectly theoretical free markets, with perfectly educated populations with 100% perfectly rational beings will be unable to solve the externality problem. http://en.wikipedia.org/wiki/Externality
It is known and proven. Do not give me a "Well, we'll figure it out later" bull... tell me how a free market is supposed to resolve an externality (which by its very definition is unresolvable by free markets).
Perfectly rational and greedy actors will always offload their costs onto unwilling parties. It is the job of the government to ensure that costs align up with the actors who create those costs.
If that is too theoretical for you, imagine two cities. "City Upstream" and "City Downstream" both are on the same river. City Upstream begins flushing their sewage into the river, and so City Downstream is no longer able to drink the water.
Solve this issue using only rational actors in the free market. The "Government" solution, is to have the Federal Government create Water Treatment plants, and then force "City Upstream" to use them. Afterwards, you tax both cities to pay for the treatment plants.
Your turn. Come up with a free market solution without the use of a central government or centralized 3rd party. Assume both cities are perfectly rational and perfectly selfish, as is common in these economic problems.
Good luck coming up with a solution. But if you're like any other libertarian who I've issued this challenge to, you'll probably run away.