You seem to be confusing anarchists with libertarians.
For example, motorcycle helmet laws do not prevent any external cost. Motorcycle drivers pay extra for insurance (except when the government prevents insurance companies from doing this), and the only other "externality" is caused by government action (forcing ERs to service people who don't have insurance). I don't know enough about sarbox - what externalities does it prevent?
Libertarians may differ on things like regulation of drilling. Some believe the externality only exists when the harm actually occurs (and should be handled by tort law), while others believe the risk of harm is an externality(I lean towards the latter).
But I'm pretty sure the boundary between libertarian and anarchist is when you call for the government to stop protecting people from the bad acts of others.
This is why libertarian arguments always become absolutely ridiculous when you try to apply them in the real world. In what world would an ER turn away someone with a massive head wound because they don't have insurance?
Sarbox is intended as a fraud prevention scheme. Libertarians tend to be opposed to it on principle because hey it's just creating a bunch of extra unnecessary paperwork, drag on the economy and all that. If corporations aren't committing fraud, why do they have to do all this unnecessary work and let the capital-G Government snoop all over the business? All fair points until Enron and Worldcom collapse and blow up a million people's retirement funds. I'll take the drag, thank you. (actual implementation of sarbox could undoubtedly be improved).
You might be right about that boundary, but it's all in how you define bad acts. I'm glad that you see the risk as being an actual thing (5% chance of it means you caused 5% of the damage, statistically speaking, even if someone else drew the unlucky number).
I suppose it's all in how you define externality too. I'm all about hiking up the gasoline tax by 2-3 bucks a gallon over the next decade. We have a trillion dollar defense budget, a boatload of strategic issues and dubious alliances all based around oil - those aren't priced in, and that's why we have such a hard time getting off of it. But most libertarians would probably tell me that that's a perfectly functioning market, oil even gets traded on commodity exchanges, how can that not be a market? It's all in your frame of reference, I guess.
Libertarian != Anarcho-capitalist
Stop trolling.