That being said, the actual carbon cost for the van vs the helo is not just covered by the vehicles, as that lame web site describes. The van needs a road, and that road needs a grader, paving trucks and an entire infrastructure of police patrol, tax guys, repair crews, fencing, gasoline stations and such muck to keep it operating. These all add measurably to the "carbon toll" of that van, but are counted as zip.
It's a good point, the point being that the calculations are complex, more so when taking into account shared resources like the ones you cite.
I think the best example of this recently was when it turned out flower miles were too simple as a measure of energy use:
http://news.bbc.co.uk/1/hi/uk_politics/6356383.stm
I hope over time goods and services will move to being dual-priced, both in money and energy terms with similar accounting audits. Consumers can then make more of an educated choice. And aviation is just another service, there's nothing unique about it bar some of the international tax agreements.
Bottom line: In 2050 when there are expected to be 9 billion people on this planet and many of them wish to share the living standard (equate that to energy use) of those reading this forum, even if you choose the convenient belief that co2 risk is small, do you want to gamble the only planet you have?