radiation vs contamination

Why does it make no sense to compare in-flight radiation exposure and ingesting radioactive isotopes?
Background Clarification:

Why Radiation and Contamination Is Like Comparing Apples and Oranges

Why does it make no sense to compare in-flight radiation exposure and ingesting radioactive isotopes? It is wrong to compare internal emitters with external emitters, ie, ingesting radioactive isotopes versus in-flight exposure or background radiation. It is like comparing warming oneself near a fire versus eating a red hot coal. Physicians for Social Responsibility in the United States recently issued a statement asserting “there is no safe level of radionuclide exposure, whether from food, water or other sources. Period.” There are a number of different types of radiation, including cosmic radiation from space, terrestrial radiation which is emitted by radioactive elements in the ground, and man-made radiation such as that released by the detonation of an atomic bomb or by nuclear reactors in meltdown.

Essential Difference

Further to the ATCA briefing, "San Francisco Rainwater: Radiation 181 Times Above US Drinking Water Standard" many have pointed out that the University of California at Berkeley "Rainwater Sampling" chart shows even at the peak finding of 20.1 Becquerels per litre, someone would have to consume 134 litres of that water in order to have the same exposure to radiation as they would receive by taking a flight from San Francisco to Washington, DC. With respect, we consider this comparison to be utterly misleading. Why? If living beings are exposed to radioactivity indirectly versus if they ingest something radioactive, the total effect is remarkably different. Radiation and contamination are not the same thing! Taking a flight will expose one to cosmic radiation not radioactive contamination.