Well, then, I've got good news for you: You don't have to rely on "belief" on this point. Stuff is actually spelled out in real documents, there for you to see and actually KNOW.
The aspects you're describing -- plagiarism, alterations of attribution -- are covered by a part of copyright often referred to in law as "moral rights."
However, the essence of copyright pivots on a single point: The copyright holder -- who is not always the original creator -- has the exclusive right to copy and distribute the work. You don't have to have profitted from distribution, or committed fraud, to have violated copyright.
No one is saying P2P technology should be illegal, or that copyright holders should have control over it. They're simply saying that copyrighted material cannot be copied and distributed without authorization of the copyright holder.
It's all so very simple.