It makes a lot more sense for Big Ag to "prove a negative" so to speak. Let's keep in mind that these corporations (Monsanto, Dow) have a dubious history of producing extremely toxic chemicals (Agent Orange) without ever accepting responsibility for the health effects their chemicals caused. See Monsanto's website for their denial of Agent Orange health effects.  It is only logical to demand we take precautions to protect us from corporations with such a reckless history of disregard for human health.

The problem with the legal and scientific burden of proof falling on the public to prove the ill effects of Monsanto's chemicals is that it would take decades of studies to produce ample proof of medical conditions caused by these chemicals infiltrating our air and water. Think about tobacco and asbestos litigation as an example of the length of time people would have to undergo exposure before having a legal remedy that still doesn't make up for the ill effects they've suffered.