Parkinson's disease is caused mainly by environmental factors. The weed killer paraquat may be one of them, and farmers who used it are suing.

Lawsuits and damages are not a very good method for deciding whether a chemical is safe to use. The US does it this way for lack of a better system. The absence of a national medical system means that the people affected by expensive diseases desperately need to sue someone and collect damages to pay for their treatment.

With a national medical system, the people who are sick would get treatment without suing. The determination of whether any particular chemical is responsible for the disease, and the decision of whether to ban it, could be made separately.