Credibility isn’t the legal question at issue. The legal question is whether or not bloggers should enjoy the same legal rights under media shield laws.
My initial reaction is that they should. I do, however, see the potential for inherent abuse if they are shielded.
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.