In a P2P network the availability/integrity of the archived material depends on storage nodes not under the direct control of the archivist. I might trust a P2P network for content re-distribution, but I wouldn't trust it for long term storage.
You don't have to; If you would be hosting the archived material yourself anyway, there is no negative I can see in doing it through a P2P network. Long-term storage could still depend on you and any other users helping with any of the content for any amount of time would just be a bonus.
