The Cowardice Argument against Pseudonymity

One of the arguments brought against pseudonymity that always puzzles me is that it is more 'cowardly'. I never see anyone develop this into anything of substance. Is it really the case that smearing someone on the internet (which, after all, is a pretty attenuated medium whatever name you use, not a face-to-face encounter) while using your own name is less cowardly than doing so under a pseudonym? Or is the idea that there is real evidence that pseudonymous bloggers are massively more likely to smear others than people blogging under their own names? I confess I'm very skeptical of both suggestions; the latter seems to me to be straightforwardly false, and I see no good reason to accept the former. Or is the idea simply that there is some sort of evasion of accountability? Within the blogosphere itself there are no mechanisms of accountability: it is self-policing. So perhaps the idea is that it is easier to get people fired for what they've said on a blog if they blog under their own name? If that's so, then we are clearly entering into territory where one man's cowardice will be another man's prudence and good sense. After all, I assume most people who think hiding their name cowardly would not think that hiding their home address is cowardly. So what principled difference is supposed to be operative here, that not only distinguishes the two cases, but would also make the former overwhelmingly on the cowardice side while the latter is overwhelmingly on the prudence side? Or if none of these is what is meant, what is the underlying reasoning?