How about some actual numbers instead of speculation?
Courtesy of Health Canada:
The risk from radon exposure for a smoker (including those exposed to second hand smoke) is much greater than for a non-smoker. For example, if you are a lifelong smoker but are not exposed to radon, your risk of getting lung cancer is one in ten. If you add exposure to a high level of radon, your risk becomes one in three. On the other hand, if you are a non-smoker, your lifetime lung cancer risk at the same high radon level is only one in twenty.
That's some good information. Enlightening even. But we have to ask, what are the odds for a non smoker who hasn't been exposed to radon? That number proves surprisingly difficult to track down. The odds, however, seem largely to depend on genetic, hereditary, and other lifestyle factors. Interesting to note that workplace factors (fiberglass, asbestos, etc) are only marginally beat out by radon as cancer causing agents.
It's also important to remember that these findings are based on "long-term, lifetime, high level exposure." Back in the 80's "high" was considered a level of 800 or more. It has since been dialed back to 200.
What am I trying to prove? What's my angle? I don't have one. I just think that if we're going to disagree a out something we should at least be aware of the basic information.