I'd be surprised if acquaintances of Appelbaum can't piece together who are making these accusations. That's the point too, they probably want to warn people without outing to the world exactly who suffered what.
But that also means there's enough info that the same people could easily speak up in Appelbaum's defense if the allegations are untrue - since they're a lot about stuff he's done in public. They haven't so far.
Without specifics, there's not enough information in the allegations to attempt to speak up in defense - if you didn't personally witness one of these alleged assaults, you would be loath to say they didn't happen on a different occasion. Perhaps Appelbaum is careful in choosing victims, perhaps the assaults never happened. You just don't know, so you say nothing.
Putting specific details to the allegations on the other hand would make that quite possible - a lack of defense in that case would be an indication that the accusations were true. But without specifics that's not the case.
But that also means there's enough info that the same people could easily speak up in Appelbaum's defense if the allegations are untrue - since they're a lot about stuff he's done in public. They haven't so far.