Yes, that is a problem. Publishers should seed the torrents and publish their hashes, thus vouching for the authenticity of the documents therein. But even if they don't, it only takes one trustworthy researcher passing the Captchas to add an open-access document to a legal archive which provides periodic torrents.

To be clear, neither Zenodo nor arXiv rejects non-open-access papers, so you cannot simply provide a torrent of arXiv papers, legally.