I love Milton Friedman. His book Free To Choose and Hayeks The Road To Serfdom swung me more towards classical liberalism than anything before or since. Friedman also did some great videos that I highly recommend. You can find the first episode of Free to Choose here
The image below is taken from Free To Choose Episode 1. It's kind of hard to ignore the literal elephant in the room here which is the tusk being carved up. Skip to 14:12 of the video to hear Milton extolling the virtues of a free markets while panning across the elephant tusk. It's quite depressing to watch. Free markets can and do lead to bad outcomes.
No one owns the elephants
In the Armchair Economist Steven Landsburg has this to say about the matter
African elephants are hunted for their ivory at far too great a rate, and these magnificent animals may be headed for extinction. While this problem may have no simple solution, it does have a simple cause: Nobody owns the elephants. An owner—any owner—would want to be sure that enough elephants survive to keep him in business. The demand for beef is far greater than the demand for ivory, but cattle are not threatened with extinction. The key to the difference is that cattle are owned. The Armchair Economist (revised and updated May 2012): Economics & Everyday Life (pp. 97-98)
I personally hate the thought of farming Elephants for their ivory or meat but Landsburgs makes a good point. Unfortunately the poachers are still killing 20,000 animals a year
https://cites.org/eng/elephant_poaching_and_ivory_smuggling_figures_for_2013_released
Knowing the elephants are there bimbling around the African plains gives me the warm and fuzzies and knowing they're being poached in their thousands gives me heartburn. Warm and Fuzzies is British technical jargon for Positive Externality and heartburn is a Negative Externality.
Externalities can be a royal pain in the ass. In the case of the Elephants they can be owned by someone or by the nation that has them like Botswana which means that there might be a neat but morally questionable solution to the problem of poaching. We might not like it, I know I don't but farming Elephants might be a solution.
Where the shit really hits the fan though is when externalities are things that can't be owned, like the air we breathe or our climate.