First, I have three points. Those points are not directly related to each other except by the fact that both points are about Mr. Hickman's complaint.
The first point is that the reference to 9/11 in the complaint is unwise. Not because a parallel can't be drawn between evil and evil, but because frankly the level of evil we are talking about here is of completely different levels. Making a reference to 9/11 does not clarify his position. Instead, it obfuscates it. Making a reference to 9/11 just gives people an excuse for missing the point. Even for people that are inclined to agree with him about his overall point, 9/11 is such an emotionally charged subject that any comparison between it and gaming is frought with difficulties. So just forget about the fact that Hickman begins his complaint with that overused word 'terrorism'.
Second of all, Mr. Hickman is not some innocent ignorent person unaquainted with evil, gaming, life, fantasy or writing. This is a guy who callaborated in the creation of most of the villians that are currently being voted on as best villain in gaming. To make a loose comparison, claiming that Hickman is some sort of pansy because he has strong moral convictions is like claiming Orson Scott Card (another author from the same background) is a pansy that is unfamiliar with evil and afraid to depict it. Those of you that are dismissive of him only make yourselves appear foolish. Maybe this wasn't his best written piece, and maybe you don't agree with him but no one has yet presented on this board anything like a rebuttal of his complaints. Instead, we see the same sort of mistakes made in this thread that you are so angry about in his editorial - emotional reaction, hyperbole, demonization, etc.
Thirdly, all that said, I pretty much agree with Mr. Hickman. There is no point in having an RPG supplement about 'vileness', I find the lust that exists for such material appalling. Labeling something 'mature content' does 9 times in 10 mean that the content is immature, base, purile, and so forth. Shock sells, but shock for the sake of shock is neither deep nor art and seldom wise. It is merely attention grabbing behavior, and a mature society should not condone it as valuable expression (although it should probably gaurd against banning it completely as well). Indeed it is Mr. Hickmans attempt at shock value by referencing 9/11 that I think upsets most people.
Yes, horrific things occur in history, and sometimes an author may even want to make (within his judgement) a blunt reference to that, but I often get feeling that there is a faction out there that just wants to revel in the vileness, that feels that one is not 'cool' unless one can out Herod Herod, that isn't satisfied until they can be graphically perverse and aren't sickened by it, and seriously loves celebrating evil as a thing to be immulated and even considered as a non-evil thing. It is against this faction that I think Hickman rails, and the suspicion that Wizards has stooped to catering to this faction and its beliefs because it would be short term profitable.