I’m mostly a fan, because I don’t feel like I have to have faith.
If my instance explodes, I’ll make an account on another instance. If the Lemmy devs collectively evaporate (and neither me nor others want to pick up the slack), then I can go to Mastodon or Kbin or whatever.
Individual rogue instances can be defederated. If e.g. Reddit truely disappears over night and Lemmy were to gain mass market appeal, then I can likely find a more isolated instance with a smaller community sharing my interests.