I'm not sure this is a bad thing. Often the messenger is part of the message. For example, if George "Dubya" Bush and Hillary Clinton both said "The war in Iraq is going well," different people would find that news more believable from one than the other. Or, even better, if they both said "We'll be out of Iraq soon," well, the interpretations of how that would happen would be vastly different. Based on the messenger.
Closer to home, if someone posted something controversial about Perl 6, is it a bad thing that we take it seriously when posted by (among others) Ovid or TheDamian or TimToady, but with a grain of salt if posted by a known troll (in the spirit of not provoking a flamewar, I'll let the reader decide who they think is a known troll rather than sharing my opinions on who would fall under that category as it's not really relevant who, in particular, it is). Extend that a bit more, and we look at Anonymous Monks. These are treated with suspicion by many (myself included) just because there is an absence of credibility. Not just poor credibility, but a complete lack. There is no context to place the message against to help decipher how to interpret the words.
As for the newly invented pseudonym, there are a couple factors here. First is the possibility of a history, thus context, being created. Second, the optimism that a new pseudonym is actually not only a new member, but has gone through the effort to "officially" join the club and be included, affords them a bit of leeway on the credibility, even if it's just the context of "I joined your group and am attempting to contribute to it." There is a presumed level of commitment that grows as the use of that pseudonym shows more posts, or even more time in the CB.
If you're at work, and someone comes up to you to tell you you're fired, isn't important that you know who this person is when deciding how to react? e.g., your immediate manager, their manager, the department clown, someone you've never met, or someone with a bag over their head?