I choose to compare these two events quite consciously, because while the Western world quite quickly came to the agreement the Charlie Hebdo attacks were terrorism, it's quite easy to argue that the attacks at the Emmanuel AME church were actually worse. After all, the Charlie Hebdo attacks followed repeated insults from a group of people who quite specifically set out to provoke an angry reaction from people they viewed as moronic and beneath them. The Charleston attacks, on the other hand, were committed against people who had never intentionally done anything to anger the attacker, and even welcomed him into their church gladly. While both were obviously heinous crimes, would not most of us agree that being murdered simply for who you are is much more of a terrorist act that being murdered for deliberately enraging someone?
And yet, so many voices are cautioning us not to label what happened in Charleston as terrorism. As Glenn Greenwald so eloquently explains:
That’s why so many African-American and Muslim commentators and activists insisted that the term “terrorist” should be applied: because it looked, felt and smelled exactly like other acts that are instantly branded “terrorism” when the perpetrator is Muslim and the victims largely white. It was very hard – and still is – to escape the conclusion that the term “terrorism,” at least as it’s predominantly used in the post-9/11 west, is about the identity of those committing the violence and the identity of the targets. It manifestly has nothing to do with some neutral, objective assessment of the acts being labelled.The last sentence there really gets to the heart of the matter. The idea that someone attacks innocent people to further a political agenda is a pretty textbook definition of terrorism. However, as the term is employed in the West post-911, it actually means "Brown people harming white people."
The term "folk devil" was first introduced by Stanley Cohen back in 1972 in his seminal book Folk Devils and Moral Panics. A folk devil, as the name implies, is a person or group onto whom we as a society project our fears and misgivings. They are seen as the literal embodiment of social problems, and through the control or elimination of them, we believe we can solve the issue at hand.
Importantly, the ascription of the status of folk devil to a group or person only works when that group or person has little to no social power. This is why Muslims serve a great folk devils in the post-911 world; it's not as if they were a particularly powerful or influential group previously, and they have little in the way of social resources to fight back against the label. As such, the actions of a few can be ascribed to the group as a whole, and ridiculously unjustified sanctions and restrictions can be placed upon them with little outcry.
This is what explains the difference in the reactions to the Charlie Hebdo attacks and the Charleston attacks: the former featured a suitable folk devil, while the later did not. While I'm sure people were genuinely upset by the Hebdo attacks, it also provided a very handy excuse to yet again condemn and ostracize the folk devil of the day.
The Charleston shootings, on the other hand, do not. It would be almost impossible to make a folk devil out of white men in America, seeing as they control the government, the judicial system, the media, and pretty much every other outlet and/or manifestation of power. Instead, the dominant story becomes one of figuring out why this one specific white person did something bad. This, of course, explains why the specter of mental illness is almost always immediately raised; after all, it just doesn't make sense. We all know scary, scary Muslims are irrational murder machines, so their crimes need no explanation. But White men are the epitome of ration and reason, so there has to be some sort of explanation for how one of them could have done something so wrong. Obviously, he had to be crazy. After all, he's acting like a Muslim!
The problem is, by all accounts the Charleston shooter was not crazy, just racist. But to actually grapple with that would mean having to deal with the very fabric of American society, which as Jon Stewart pointed out, just isn't going to happen.