> The presecution claims it's not the active ingredient but the whole herbicide that's cancer causing. I think the studies are only on one of the ingredients, not on the whole herbicide?

Yes, the claim neatly was crafted to render all the systematically gathered evidence only tangentially relevant, so what you are left is a lay jury deciding what they feel is more probable (the civil standard being a mere preponderance of the evidence, not the beyond a reasonable doubt standard of criminal law) on a complex scientific topic without strong scientific evidence and with plenty of opportunity for factors which roster to the likeability of the parties to influence the decision.

Whatever the arguments are that this is a necessary thing to accept in the legal system (and maybe even desirable, in that it disincentives certain antisocial corporate conduct), it doesn't really say much about the underlying facts.