We just purchased a home and tested for radon. The level came back at 11 and I was told anything over 4 is high. It was recommended to install a radon mitigation system. Is radon really as harmful as the housing industry is leading everyone to believe? According to the article here, it is actually good for you.

Radon is not "good".  It is a radioactive gas that is considered the second leading cause of lung cancer.  And the decay byproducts of radon include radioactive polonium, lead and bismuth that can trap in tissues.  The final decay product is stable lead, which in itself still poses other health risks.