First, I'm not sure "deception" is the only thing in play here. I suspect that Siegel's career would have suffered even if he had made similar comments under his real name. Writers at magazines like Slate and TNR can engage with thoughtful commentators, but probably shouldn't get into flame wars.
Our culture has yet to decide whether Web comments are closer to "conversation" than "publication." When we talk over the phone, face-to-face, in a quick e-mail, or even on a radio talk show, we all take advantage of the wiggle room our culture gives us to embellish or to borrow ideas without attribution. In the extreme example of the talk show, we're even permitted to maintain our anonymity as we hold forth before an audience of thousands or millions.
That slack generally vanishes when we submit our comments for publication. It's understood that we can be charged with plagiarism unless our written comments are original or properly cited. Editors traditionally extend anonymity to those who may get fired or firebombed for what they write. Accountability demands that everyone else put their names to what they write.
I regard Web comments as something closer to publication than conversation, so I use my real name or something that identifies me—ShaferAtSlate, to use one recent example—when posting. But I understand the millions who think posting is more like conversation.
This gets to what the comment boards and the Fray are about. I think BOTF poster have generally been on the rigorist side of the continuum -- plagiarism results in social sanctions. But are all of us whoe post psuedonomously engaging in some form of deception?
I dropped my star and then particpated in a thread, giving some people the mistaken idea that I was a newbie. Then I switched to a different handle altogether since I thought it unwise to use a handle derived from my real name. It seems to me that these "sins" pale in comparison to what Siegel did, since I wasn't using the pseudonyms to try to bolster my own reputation.
And that's the bottom line -- what Siegel did was dishonest, but, perhaps worse, it was lame.