Don't have enough time to read whole thread, but here's my .02 BTC:
1) Make sure we're talking about non-pecuniary externalities, and make sure to define that. Because basically every market system operates on constant pecuniary externalities, its just that it often takes some work (and transparency!) to figure out why something costs what it does.
2) For the purposes of this thread all should read Coase's paper on externalities. Externalities are solved by markets when transaction costs are low. Thus, it would be more productive to talk about what externalities have high transaction costs, and then figure out how to lower those costs, or design some alternate system that is manages the problem ethically and equitably.