Let me tell you a story. I have a friend who is a devout Christian. I wanted to show him this anime that I personally thought was a great show. I said "It's called Fullmetal Alchemist: Brotherhood," to which he replied, "Alchemy? That sounds demonic." But he was willing to at least give it a couple episodes.
Once we reached the Nina episode (#4 or 5?), he walked out and began to tell everyone how demonic it was.
I'd like to give a response to others who may feel this way. My friend thought it was demonic for a couple different reasons: 1) the darkness and gruesomeness in the first couple of episodes, 2) alchemy in general, and 3) the vague "Christian" allusions in episode 2 and Edward's atheist spiel.
As for the first reason, I admit it's intense, but I think that's more of a pacing issue than anything. As Brotherhood is a re-make of the original (and the original actually followed the books fairly well for the first 25 episodes or so), the Brotherhood writers decided that condensing 25 episodes into 7 was going to be better than re-hashing the whole first arc scene for scene. This makes newcomers to the series understandably uncomfortable as it is pretty gruesome, and it may have been a mistake on the writers' part. But it's a pacing mistake, not an issue with the show's core values.
As for the alchemy issue, the "alchemy" in FMA is not real alchemy in any sense of the word. It's a magic system like you'll find in any fantasy story, and (as this friend is an Avatar fan), I'll mention as well that the magic of Avatar was heavily inspired by Fullmetal Alchemist, and the creators of Avatar are actually huge fans of the series. This isn't too hard to see, since a lot of the fight scenes look a lot like the element bending of Avatar, so I won't go into that. The word "alchemy" is used so that the author Hiromu Arakawa could make the connections to scientific advancement that play such a heavy role in the themes of the show. This brings me to the third point.
Episode 2 of Brotherhood shows a town ruled by a tyrannical liar who plays the part of a religious priest. Some vaguely Christian terminology is used by him like "divine grace" and "resurrection", and my friend took this to mean that the show was anti-Christian and demonic. Add to this that Edward has his smug little spiel about how science is taking the place of religion. On a superficial level and to an American audience, this may appear anti-Christian, but I'm arguing that it's not. The motivation is character development and theme development. There are several points to make here.
Firstly, the show was intended for a Japanese audience in a country where Christianity has very little presence. The author is not anti-Christian (as this is the only time I've seen anything resembling Christianity in any of her works), and many people would not even make the connection that these words like "grace" and "resurrection" are allusions to Christianity. It would be like someone in the US having a show where one episode denounces something that vaguely resembles Buddhism. Frankly, no one in the US is going to care, because most people in the US don't have strong opinions on Buddhism, unlike Christianity, which is quite the hot topic these days. I think the same principle applies here.
Secondly, and more importantly, Edward's atheist spiel is a set-up for his character development. To be concise, the entire show is about people who are arrogant enough to think that they can "become like gods," whether it be through science, religion, or what have you; and every single character, exhibiting this mentality, has to pay the consequences for their arrogance. It would be ridiculous to assert that the author sides with Edward's pro-science argument when she follows that episode with instance upon instance of science being used for horrible, monstrous things. The author is actually making a point that many Christians would actually agree with, which is that scientific advancement often results in humans meddling where they shouldn't. In reality, it's the foundation for a story that is going to critique scientific advancement, which I think Christians wouldn't mind listening to. Not only that, but Arakawa also shows us in that episode that Rose and Edward are really the same in a lot of their motivations. Ed thought that if he studied hard enough, he could bring his mom back to life. Rose thought that if she said enough prayers, then her boyfriend would come back to life. Just another instance of humans thinking they can be in control. The thing is, no devout Christian thinks this is how Christianity works. Christianity isn't about giving your prayers as currency to God and expecting a service in return, but whether or not Arakawa knows that isn't the point. The point is that, Christianity or not, that belief is arrogant and futile, and I think we can all agree on that.
The show is not anti-Christian; it's anti-arrogance.
In the end, Fullmetal Alchemist is promoting the strength of familial bonds, friendship, and humility. And it doesn't pull any punches in showing you the consequences of human pride. You don't have to like it - as it is intense - but it is not anti-Christian, and it is not demonic.
Listening to: Fullmetal Alchemist OST
Reading: Harpist in the Wind