Well, like anything else,
WH40k can be seen as a good thing or a not so good thing. It should be kept in mind that it is loosely based in real history. The whole setting is like early middle-ages where a technologically and morally depressed empire is trying to discover information from the golden ages (DAoT and Antiquity) The empire is constantly struggling with enemies threatening it from all sides (as the Roman Empire was during its crumbling) and trying to prevent "heresy" from spreading in the realm. There are also sooo many more references to different eras in history which can be seen in all of the races, like 17th-century-like infantry, ancient Egyptian references and many more. The setting is chaotic and dark because history is chaotic and dark.
Sure, if you look it from the right angle you can also see the "satanic" and "corrupted" stuff, like the ultra violent religious system, wasting millions of lives for a piece of trash from the Dark Age of Technology or soulless monsters bent on consuming all life. To an outsider this may seem rather chaotic and shocking. But that is only the tip of the iceberg. Under the water there are a lot of interesting and imaginative details and a well thought out story, instead of just a barbaric and mindless universe full of violence and war as an outsider might see it on the first glance.
I bet no one is worshipping the Emperor or the Dark Gods in real life or hatching dark and violent thoughts in his head. Even if one does, the guilt cannot be entirely placed on a fictional game's shoulders. Sure it can advance that kind of things, but it does not turn people into screaming, violent fanatics. It is easy to blame the game for the mistakes of players. (No pun intended)
And the whole Nazi argument is just silly. Yes, there are some pretty bizarre people around, but hey, it is just a game for crying out loud. My gaming group includes two black persons and one asian. No one ever looks them funny or treats them in ways which could be seen as racism. Besides the most racist place is the Imperium, if you do not like "racism" you can always choose one of the more tolerant races. In my opinion, playing a game is hardly being a racist. I would inderstand if there were swastikas and people yelling "death to the ni

ers!"
As the writer insightfully notes, some people playing the game are rather socially awkward and "nerdy". But so what? I have met more disturbing people in the mall than playing a wargame. As I said earlier, there are all kinds of people playing wargames and the writer was clearly biased in my opinion.