I do not think a belief in something like Christianity is necessarily intrinsically evil - although I am willing to consider, as Nietzsche did, that it might be. A belief is simply an interpretation of reality, after all, but it is not “real." Or, that is to say, it is only as "real" as we choose to make it. The problem comes when we start wanting others to accept that our beliefs are "real" and theirs are not.
Generally, a belief can be good, bad, or neutral; but sometimes it is hard to tell the difference, and sometimes even a "good belief" can be believed in so strongly it actually becomes a "bad belief." And one of the ways this happens is when that "good" belief is held so strongly that it can be used to cover up any number of evils.
For example, even if the Christian "belief" was proven to be perfectly true and intrinsically "good," it was still people's blind devotion to that "truth" that led so many of them to either conceal, or pressure others to conceal, the child sexual abuse in the Catholic Church. Pedophile priests, in other words, used people's devotion to their faith to prey upon their children. And all because these parents, once the abuse had occurred, were more interested in protecting their "beliefs" and their "church," than they were in protecting their own children, or even the children of others.
Such concealment, by both friends and family alike, was not the result of indifference or malice toward the victims, of course, but was simply the result of fear. After all, what would they look like to their deeply Catholic friends, and how would they be treated in their deeply Catholic communities, if they were to accuse the church - and in a sense, God - of so vile an act? And even worse, what would happen if they could not prove their accusation in court? Indeed, just think of how difficult it is for a woman to report being raped, and for some, accusing the church of raping their child may seem even more difficult than that.
Marlon Brando talked about this kind of devotion to a belief in the documentary, "Talk To Me, Marlon." He was commenting on how Americans had bought into the lie that was the Vietnam War, as the release of the Pentagon Papers in 1975 by Daniel Ellsberg would later prove. "They had these people so hog-washed," Brando said, " that rather than alter their beliefs, they sacrificed their children." Rather than accept the idea that their government was lying to them, more to the point, they choose to send their sons to die in a war on the other side of the world; and all for the "love" of God and country.
Another example would be when a belief in a peaceful, self-sacrificing Christ is "believed in" in such a way, and with such blind devotion to those who claim to speak authoritatively for that belief – whether it be Hitler or the Pope - that whole societies of Christians think it practically their moral duty to either burn witches for God (as they did in the 16th and 17th centuries) or kill Jews for The Third Reich.
To put it in Christan terms, then, a belief is “bad,” therefore, whenever it becomes the mob mentality of the majority, and is then used as the measure of all moral “truth,” for everyone, in everything from sex to how one should keep holy the Sabbath – even if they would rather not keep it holy at all! It is also bad to the extent it hurts and divides (which, to me, is symbolized in the pain of Christ and the “dividing” of his garments, as well as the division of his blood from his body – hence, death - which are also symbols of the the suffering of the Jewish people via the Diaspora, and so on), and good only to the extent it heals and unites (as symbolized by Christ’s forgiveness of sins and his resurrection – i.e. the re-unification of people as well as the reunification of his blood with his body).
For me, in other words, any belief that separates people in anyway, is bad, and therefore deserves - indeed therefore needs - to be questioned, as Nora Bateson put it in her documentary An Ecology of Mind, “until it bleeds with the authenticity of the un-separated.”