In my limited experience, that has no bearing in a copyright case - if you use it, it's your responsibility to ensure you have the right. I've filed and won two cases in the mainstream internet world. For most judges, it's an open and closed case, you had my material, I can prove that it's my material, you knew you weren't the creator of said material, you can't prove that you had the rights to use said material, you pay.
It's just like walking out of the store with the goods in your pocket - it's fucking steeling - even if someone else put the stuff in your pocket.
And YES we need to get the fuckers that are steeling our material - along with the "enablers" - and if the "enablers" are out of our reach, so be it, the fuckers steeling it (consuming it) still need to be fucking burnt.
Every time one of us says it's OK, for whatever lame fucking reason, we become part of the problem. I've lost count of the people in this industry who have proudly announced that they have never paid for a download (music, porn, software) because they know how to cheat the system. Now is that the type of person you want make business plans with? Not me!
When are we going to quit saying that we can't stop it so it's OK - IT AIN'T FUCKING OK.............