While I agree problems from radon exposure are a bit ambiguous, there are reasons to abate radon in a home. Resale is one reason, insurance can be another, and peace of mind is the third.
You have actually done the second step in passive abatement already. If you were to bury an H pattern of perforated 3" or 4" PVC pipe and hook that to a stand pipe that terminates above the roof line, then replace the plastic and seal any place where the plastic touches pipes or concrete, you will have made the minimum passive system.
If the area is rock to the point burying a pipe is not feasible, lay the pipe on the rock and secure it. Then add the stand pipe and seal the plastic.
Actually, adding vents and a small fan on one side of the crawl space can also pervent radon from entering a home.
Radon is a heavier than air gas and is actually not the bad part of the situation. Radon is a radioactives gas and begins to decay. The compounds created after the decay cycle starts are the problem if they get into a persons lungs. Most doctors/scientists think many years of exposure are necessary to see any negative effects from radon exposure.