[dragonwriter]

Arguably, any system of assessing and forcing people to pay for the assessed external costs is at odds with capitalism (it is arguably a form of central planning and interference with the free market).

Which is not to say that it isn't a good idea, and the minimum deviation necessary from capitalism to address externalities, but ideological capitalism/free-market purists tend to oppose it pretty strongly.

[saulpw]

"Capitalism" does not mean "free market". It literally means that the profits go to investors (capital) instead of to the workers (labor). You can certainly have a capitalist system that does not have a free market, and you can certainly have a free market system that is not capitalism.