"The only purpose for placing copyrighted works in the shared folder is, of course, to 'share,' by making those works available to countless other P2P networks," the MPAA wrote.
You know, that assumption most likely is correct.
However, an assumption is never grounds for legal action, even in civil court, unless there is a preponderance of other evidence to suggest the defendant is guilty. I would not venture to say that a statement like the one above constitutes more than a 50% level of doubt or certainty. Now, if they track packets and look for TCP receipts that yes, this person indeed made these files available and yes, somebody else downloaded them; I would say there is grounds for action then. It's an issue of principle rather than one of practice. Sure, the intent might be pretty clear here. But if we let this type of "lack of evidence" ruling become commonplace in civil court, it's only a matter of time before "beyond reasonable doubt" becomes "meh, maybe he did it, but I think he wanted to".