There is a ploy practiced by many atheist of the type who inhabit places such as the Secular Web and Infidel guy. It's been so institutionalized it's almost a mortar. In fact I've seen this kind of things so many times now, when the Christian apologists get together they can stamp it out, but no soon will they rid the net of one institutionalized atheist fallacy, than another will rear its ugly head.
The fallacy to which I reefer here is the "No true Scotsman," fallacy (NSF). I dot' know the etymology exactly, but the general idea is that in the heat of argument one is likely to say something like "no true American would ever (do whatever)" The way it's used is this:
Atheist claims something like "Hitler was a Christian." The Christian makes the mistake of saying "O but he wasn't a true Christian because bah, so the atheist says 'that's the NTSF So without even thinking about it, they just dogmatically declare anyone was ever a Christian of any kind to have always been one. Once a Christian always a Christian (unless you become an atheist a post on the secular we) and then anything you do that's negative pertains to Christianity as the upshot of being a chrisiatn. So Mao was a Christian because he heard a Bible verse once, therefore, Christianity makes you become the Chairman of the Chinese communist party and write little red books.
This has become such a mantra that it cancels any kind of critical thought. Anytime any apologist comes near any sort of questioning as to one's Christian credentials the atheist says something like "I hear bag pipes playing." We need to make up a Nam for the fallacy of calling everything the no true Scotsman fallacy. What really amusing is that they are using the fallacy in the wrong way, as though they dot' really know what it means! The true fallacy is aimed at people who try to use patriotism to win arguments. No true American would call for pulling out of Irk (or Vietnam or whatever hopeless mess we've gotten ourselves into this decade). But that is not the same saying that any time one says "so and so Is not a Christian" it's the fallacy. That fallacy has nothing to do with the commitment level of a particular individual. It has to do with the way in which I construct another perinea's commitment level. If the commitment level of an individual can be demonstrated toward some affiliation then obviously that person can be said to be or not to be "a true so and so" (whatever it is). The only requisite criteria would be that there must be clear guidelines as to what a true so and so is about. That's why the no true Scotsman thing is a fallacy, because there is no way to know what a true Scotsman would say about any given issue, since being a Scotsman (or an American) is rarely a voluntary affiliation. Of course there are cases in which we CNA say no true Scotsman would do X and it not be fallacious. Fore example; no true Scotsman is born in China of Chinese patrons who no relation of any kind of with Scotland and who have never been to Scotland. Such a person hardly had any claim to being a Scotsman, but even in such a case the idea of being a Scotsman is still rather vel. Perhaps one coulee be a true Scotsman if one pinched pennies, played golf, kept sheep, ate fried Mars bars, and wore lad, even if one had never been to Scotland and was not Celtic origin.
The idea of being a Christian is a bit more voluntary than being a Scotsman, thus it is a big less difficult to pin down. This is true, moreover, because Jesus did says something about what is followers would do and would not do. We can say "no true Christian would be anti-Semitic" since Christ was Semitic. Since worshiping Jesus of Nazareth as the son of God is part of being a true Christian, and this is stated in the manifesto (the Bible) then we just might conclude that one who doesn't' do that is not a Christian. Moreover, the church itself laid down guidelines for being member of the Christian community (the church invented the word "Christian" not Jesus). Those guidelines are embodied in the creeds. So in fact yes we can exactly say with no fear of contradiction or of fallacy that no true Christian would ever say anything contrary to the creeds. Because to say that is to be an untrue Christian. Paul said no one by can say by the power of the Spirit "Jesus be cursed" (1 OCR). He was not committing the no true Scotsman fallacy. He was laying down a statement of spiritual fact. So we can say based upon this fact, "no true Christian prophet can say by the power of God that Jesus is cursed." This is a factual statement, given the assumptions of Christian belief. and not the NSF.
It would not be smart to concentrate too hard on stamping out this silly mortar of the atheists. They will only replace it with another. In the mean time, we know to deal with it, we can always use it to our advantage. If it is a fallacy to argue that so and so wasn't' a Christian, because Christianity is very diverse and we can't say who is and who is not and the attempt to try is always a fallacy, then it must also be the same fallacy to say "all Christians do x." The idea that Christianity causes all these social harms and leads people to be right winners is also the same fallacy.