I can't tell how universal you think this is, or what kinds of community, harms, or participants you're thinking of. My general feeling is there is so much variation on so many dimensions that it cannot be generalized to this extent.
I also feel, for many informal communities (that is, not legally constrained), this focuses far too much on fairness and fear of legal reprisal (defamation? pretty much never matters except in extreme cases). It also focuses too much on what exactly happened, rather than how many participants feel about future interactions. Local uncoordinated bans of unpleasant people is probably enough in most cases, especially combined with private conversations among the authorities of different local events about what to watch for (sharing evidence, rather than results).
Let's say you're concerned about someone in your community, and are putting together a post detailing why you think others should be concerned as well. This sort of documentation is a core part of decentralized exclusion, how a large community without any formal leadership can still kick out bad actors. As part of writing this you're talking to people who they've have hurt, and your sources are understandably nervous about retaliation. Some of that is unavoidable, since once the post is public the accused will likely be able to tell a lot about who your sources are from what information you include, but there's also the issue of retaliation against your sources to keep you from publishing.
One way you could handle this is just to publish without giving the accused any indication that this is happening. I think this can very occasionally be the right decision, but not offering the accused an opportunity to point out places where you've gotten the facts wrong gives up a lot:
But then what can you do? How can you give the accused a chance to privately dispute your claims while minimizing the risk to your sources that the accused will pressure them into getting you to abandon publishing?
While I haven't tried this, I think this should be possible to address with precommitments. You talk with your sources and get together what you think will be the final draft. When you write to the accused you include something like "to protect our sources from retaliation aimed at keeping the serious allegations in this post from becoming public, we have agreed with them that from the time we first share a draft until the post is published we will not honor any requests they make to withdraw claims." Imagine:
Author:
I can't publish these accusations without letting the other side raise potential counterevidence.
Sources:
We're afraid of retaliation during the period when the accused knows this is coming but before it's public, with the goal of getting us to retract.
Author:
I'll commit to not honoring any requests you make to withdraw claims between now and publication, and to make the accused aware of this, so they know retaliation won't achieve their goals.
Let's say you try this, though, and a source does come back to you during pre-publication fact checking:
Source:
[to Author, in advance] They asked me to bring drugs into the country illegally.
Accused:
[to Author, in fact checking] I did, but the drugs were over-the-counter medications and I thought this was legal.
Source:
[to Author, after fact checking has begun] Accused told me about the drug thing and asked me to retract my claim. I probably should have mentioned that they were OTC and they didn't know it was illegal.
With this strategy the author would ignore that the source agrees with the accused's clarification. And would also ignore it if instead it had been:
Source:
[to Author, after fact checking has begun] Accused told me about the drug thing and asked me to retract my claim, but they're thinking of a different time; I was talking about the opium.
If it's important to the source that the accused cannot retaliate against them to shut them up and they've decided to use the precommittment process I'm proposing, this requires giving up some flexibility. In this case the time to get clarity from the source on exactly what they're claiming would have to be before starting the adversarial fact checking process. Once it has started, all you can do is consider what you've heard from the source before fact checking and what you're hearing from the accused now, and choose between keeping the claim, weakening it, clarifying it, or dropping it.
Note that weakening it is quite tricky: you can't do it in a way that makes it sound like the source is claiming something different than they already endorsed before fact checking, so if you do want to keep the claim I think clarifying it will often make more sense. In this scenario I think I'd go with something like "my source told me the accused asked them to bring drugs into the country illegally. During fact checking the accused agreed that it wouldn't have been legal, but also said they were over-the-counter medications and at the time they made the request they believed bringing them in was legal." And then potentially adding "Due to the precommitments to our sources I described above, I have not asked whether my source agrees with this description of the situation, but even if the accused is correct I think it demonstrates a reckless attitude toward bringing controlled substances between jurisdictions."
Overall, this seems like it should work, but as I said above it isn't something I've tried. One way it seems like it could fail is that the accused might not believe that the author really will ignore anything they hear from the sources pre-publication, so I think the author might need to be especially clear with the accused and perhaps have a reputation of sticking to this sort of thing. I could also imagine the accused irrationally retaliating against the sources, but since that could also happen post-publication that seems like an unavoidable risk of sharing important information about someone vengeful, and not a downside of sharing something for fact checking? Do people see other ways this proposed mechanism would be likely to fail?
Disclosure: while I'm on the BIDA Safety Team I'm speaking only for myself. My wife is on the Community Health Team at CEA, but I haven't run this post by her and don't know her views.