Mind you, most peer-to-peer sharing protocols work by having everyone be distributor and downloader at the same time.

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)

Maybe you could argue that doing so for profit is different legally but its hard to argue that freely enabling others to do what you are doing is fundamentally ethically worse than doing so yourself.

I don't think there is a fundamental moral right to a particular pattern of bits in the first place to defend.

I'm interested in your view on how it is an ethical difference.

You mean like the pirate bay?

we're in the weeds now, but: sort of. the pirate bay doesn’t distribute anything — it just indexes it — but actually getting content via the pirate bay involves torrenting the content. and torrent is a tech that makes every downloader also an uploader to peers.