My point is exactly that the credibility of the source should have no bearing on the legality - the only real difference between a “blogger” and a “journalist” is one of credibility (deserved or not), and as that is subjective, the law should apply equally to both in order to not be capricious.
A blogger - or a journalist - who abuses their protections will suffer a loss of actual credibility and may subject themselves to civil liability in some cases. Any protected activity or right can still lead to criminal or civil penalties if they are abused.
Certainly, credibility has no bearing on the legal question.
You said, “The blogger should have to earn the trust of readers before they should accept anonymous or confidential sources at face value.” My point was that earning the trust of the readers isn’t relevant to the question of whether or not bloggers should be shielded.