Personally, I found the whole "Vile Darkness" thing, not offensive, but "meh". There were some good ideas in the collection of hardcover book and magazine articles, but other than some creepy pictures in the hardcover, nothing struck me truly as "eviler than evil". The attempt to bring adult content to the D&D game was a good idea, IMO, but not well handled. Not in an "my-god-what-of-the-children" sort of way, just in effectiveness.
That some found the attempt offensive was not surprising, and fair. D&D caters to a wide audience (in a niche hobby, parse that!) and many prize its family friendliness.
That Hickman was offended, worried about the direction of the hobby, and decided to speak up was fine. But Hickman went over the top in his criticism. With the use of the word "terrorist" and really, his whole diatribe.
Now, nearly 10 years later, it's a footnote in D&D history and all involved parties are pretty much over it. Except for the easily excited hardcore fans on the interwebs! (and yes, that includes me) Decker wasn't trying to be negative on Hickman in the recent interview, but rather just the opposite. And to criticize him for misremembering the exact details of Hickman's rant nearly ten years prior is silly beyond imagining. And Decker was close enough. It's a charged word, often overused (certainly in this case), and tends to stick in the brain when someone uses it to attack you and/or your work.