Both the CDC and The American Lung Association recommend maintaining a 50% or lower Relative Humidity level in your home, AND recommend ventilating polluted indoor air with fresh outdoor air. This will reduce the negative effects of moisture on your home and family.
In addition to moisture, RADON can also enter your home through an open system. Radon is the second leading cause of Lung Cancer in the U.S. http://www.cancer.org/cancer/cancercauses/othercarcinogens/pollution/radon
Radon breaks down into other elements. During the breakdown process, alpha particles are released. This is radiation, and it can damage your cells DNA. So if you have radon, you have radiation in your home. What level of radiation is acceptable to you and your family? Radon enters through openings and weaknesses through your foundation walls and floor. Installing an open system is essentially creating a freeway for radon. Open systems can also compromise the effectiveness of existing Radon Remediation Systems.