We're allowed to form judgments about people based on evidence that wouldn't be sufficient to convict them of a crime. The consequences of me forming the opinion that this guy is a domestic abuser are far lower than the consequences of a court doing so. And of course, even courts use a much lower evidential standard than 'innocent until proven guilty' when deciding civil cases. Making a derogatory comment about someone on the internet is much more analogous to a civil court finding against the plaintiff than it is to a criminal court giving someone a jail sentence.

In any case, HN is very selective about this high evidential standard. People will make a lot of effort to give probable domestic abusers the benefit of the doubt, but pick one of HN's official enemies and suddenly any little scrap of evidence is considered quite sufficient!