I am not sure, but I think that an implicit goal of keysigning is to: one, get any chain at all between two people for the more common case of no chain compared

I am not sure, but I think that an implicit goal of keysigning is to: one, get any chain at all between two people for the more common case of no chain compared to the rarer case of active malice; and two, if enough people do it the graph should reveal impostors or at least a discrepancy that can be investigated. Someone may not realize there's a fake key out there with their name on it until a bunch of people start signing each others keys and uploading the wad of signatures to keyservers.