> I don't really know how to bridge the moral gap with this sort of viewpoint, honestly. It's like you're telling me to sympathise with the arsonist whilst he's still running around with gasoline

That wasn't how I read it. Neither sympathize nor sit around doing nothing. Figure out what you can do that's productive. Yelling at the arsonist while he continues to burn more things down isn't going to be useful.

Assuming good faith tends to be an important thing to start with if the goal is an objective assessment. Of course you should be open to an eventual determination of bad faith. But if you start from an assumption of bad faith your judgment will almost certainly be clouded and thus there is a very real possibility that you will miss useful courses of action.

The above is on an individual level. From an organizational perspective if participants know that a process could result in a bad faith determination against them they are much more likely to actively resist the process. So it can be useful to provide a guarantee that won't happen (at least to some extent) in order to ensure that you can reliably get to the bottom of things. This is what we see in the aviation world and it seems to work extremely well.