I'm not above using inflammatory language when I want to and I don't subscribe to tone-policing in general. But in the context of the paragraph you quoted, "a legion of idiots" refers explicitly to a specter in the mind of any person with code written that’s considering releasing it open source. It does not refer to any specific individual, situation, project, etc. It is a fear of the mob and of the dog-piling we so often see in open source communities.

But to continue on the topic you brought up - I am also not interested in calling out people who decide a project is not for them and decide to walk away. I am calling out people who jump into discussions about the core fundamentals of projects that they are not currently contributing to and turn those discussions in a hostile direction. Once they realize that their technical contributions are not wanted they turn to character and reputation attacks against the project owners and core contributors. Even if one out of one hundred users matches this description, you end up with a situation most sane individuals want to avoid at all costs.

So there is no invalidation of people who believe Elm went in the wrong direction. There isn't invalidation of people who wish to express that opinion publicly and even on project hosted forums, chats, bug-lists, etc. It is against those who go the "extra mile" and persistently push for changes even after they have been rejected and who resort to attacks on a person's character or reputation when they fail to get their way. And it is against those who defend such behavior by invoking some unspoken rules of open source development.