Free Market finds the way to maximize profits, therefore it is well known for its tendency to externalize as much of the costs of production as possible. This is exactly the reason why it causes so much damage to environment and people's health (e.g. factory workers, but also general public). Carbon pricing is an artificial way to try to bring some of the externalized costs back into the equation, i.e. make them internal. Such manipulation of Free Market is making it less "Free", just the same as any government regulations for worker safety, worker health, toxic material dumping, pollutant release etc.