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I'm inclined to give Klein the benefit of the doubt on this. I have no doubt that Klein has noticed the increasing use of "Serious" as irony, both in your blog and in others (notably Atrios and Digby). But it may also be true that what triggered his post was reading that particular Swampland comment.
Thus, the comment was more a "straw that broke the camels back" phenomena.
You are getting under his skin Glenn. But you have done so through the excellence of your entire work, not the content of one particular column.