There's a difference between pirating something, and distributing pirated content, both ethically and legally.
This is why they are "peer to peer". The bittorrent protocol for example downloads files in fragments, and every fragment that you have downloaded becomes available for other clients (i.e. you start becoming a server as soon as you have downloaded one fragment)
I don't think there is a fundamental moral right to a particular pattern of bits in the first place to defend.