> No True Libertarian
No True Scotsman! Just like you are closely aligned with Fidel Castro and other autocrats on all issues, because you probably believe in socializing certain things, right? :)
Libertarians are extremely intellectually diverse in their politics -- anecdotally, much more so than conservatives and progressives combined (population size adjusted). Old school Libertarians -- the ones often associated with the birth of the movement (and the ones quoted by Democrats to avoid intellectual debate) -- tend to lean heavily conservative and have an oversimplified view of either the non-aggression principle, the imperfect nature of the world, or both. Milton Friedman is an example of one of the first prominent libertarians to start considering alternative approaches for externalities.
Do I care who first coined the term carbon tax? Nope; it's not about scoring points for your team. The fact of the matter is that the idea of a carbon/pollution/externality-offsetting tax arises naturally from the non-aggression principle, as I described.
> So, for your mercury example, the libertarian solution would be for the owner of the polluted water supply to hunt down the source of the contamination and seek restitution for the damaged caused.
I didn't realize you spoke on behalf of true libertarians!
Tell me, what would you do today if someone dumped mercury in your yard? The same thing -- just because there are laws, does not mean you don't have to deal with people breaking them. And regardless, no, mercury has non-localized and criminal effects (poisoning is a form of assault). If someone threw a couch or some other localized non-poisonous pollution in their neighbor's yard, then yes, that is generally a matter for the civil courts. As it is now, even though littering is illegal.