Hubi

Even regular users can see them through other federated services like kbin AFAIK. They show up under likes and dislikes.

Downvotes are public on Lemmy fyi. There are interfaces that show who voted on a post or comment.

Of course it matters. A new network will have to start from scratch and with the “nobody is there, so I won’t join”-mentality, potential growth is severely limited. By implementing federation, you will instantly have a base community to build on.