I agree that publishing case (1) causes harm (spammers will just use a different domain if they know you’ve blocked theirs.) But case (2) is rather different. I don’t think the same justification for lack of transparency exists in this case. And I think shadow-banning the submission in case (2) is not very user-friendly. It would be better to just display an error, e.g. “submissions from this site are blocked because we do not believe it is suitable for HN” (or whatever). A new user might post stuff like (2) out of misunderstanding what the site is about rather than malevolence, so better to directly educate them than potentially leave them ignorant. Also, while Breitbart is rather obviously garbage, since we don’t know everything in category (2) on the list, maybe there are some sites on it whose suitability is more debatable or mixed, and its inappropriateness may be less obvious to someone than Breitbart’s (hopefully) is