In order to prove a product caused an injury requires many experts trained in the relevant scientific fields. Yet, it's not good enough just to have the number one expert in a field--you've got to have other experts, research, studies and the smoking gun documents from the corporation you are suing (assuming no shredding was done) to prove your case. In 1993, the Supreme Court ruled that courts, i.e. judges, would be the gatekeepers of determing what is science and what is not. This was the seminal Daubert v. Merrell Dow case. Since then, some courts have taken Daubert, and made the rules even more stringent--all to the detriment of consumers with valid cases.
Barry Yeoman of The Nation has a well-written piece on the real world effects that Daubert and its progeny have had on hurting consumers and helping corporations avoid responsibility for their bad acts.
This quote sums it up nicely:
Until significant changes take place, say Daubert critics, the system will continue to harm more than scientists' reputations--it will also harm ill and injured Americans. "We do need tools to make sure that bad science doesn't get to court," says David Michaels, a George Washington University epidemiologist who served as an assistant energy secretary during the Clinton Administration. "But Daubert is an imprecise tool, and its application has resulted in miscarriages of justice."