Th fines are not just. It's just politicians catering to Hollywood.
However , that download defense don't work. If they find childl porn on your PC , that defense would not work. Best be careful who you let in your house on your computer.
So fine them back? If they dont have to prove it, you dont have to either.
No they cant, but there are no law agenst do a mass mailing against the guilty and the innocent, obviously some of the guilty person pay up to avoid a court battel out of fear or conscience (they are after all guilty), not knowing how hard it is to prove the crime, especially when entrapment is illegally in most civilized countries.
As long as a innocent person not go to court and do battel, it cost WarnerBrothers noting to make sweeping accusations, and time to time they will take a "normal" guilty person to court to make a exampel of him or she, even if they cant prove anything they can drag out the negotiations forever, pay a smale sum now or endure this crap for several years and risking paying a large amount in the end.