There is a very odd, but unnerving, phenomenon that I have seen my entire life, but which has only started to really bother me recently (because, well, I can be kinda' dense), and I was prompted to write this by a conversation I overheard while in a Coffee shop in Lancaster earlier this week. This phenomenon of which I speak is the tendency for members of a religion to point to other members of the same religion who simply aren't in lock-step with them, and shout "they are not a real member of the faith!" In the U.S., it's most common to hear that someone is a fake Christian so that's what I'll speak of directly here, but you'll also hear it used to refer to members of other religions as well.
Now, I'm an outsider to all religions, so it may strike you as odd that this would bother me. However, this bothers me for a few reasons. The first reason is that it is simply arrogant - yeah, that doesn't affect me, but it annoys me. Really, the only way to know that someone is not a true Christian is to know that they don't believe in Jesus, and are therefore, by definition, not a Christian. Otherwise, you may take issue with their view of Christianity, but it's astoundingly arrogant to claim that they are not Christian simply because they disagree with you on issues of charity, gay rights, war, gun ownership (yes, I've actually heard this one, I didn't know that Jesus was overly concerned with firearms, it must be in the Apocrypha), acceptance of scientific discoveries, etc. etc.
Most of the time, the arguments are either over issues that the Bible doesn't directly mention or is vague about, or issues where, based on the Bible, you could argue many different points of view. However, most people have a set of beliefs based on their experience and/or the teachings of their particular clergy, and they are unwilling to accept that someone who believes in the same scripture that they do might interpret it another way. It really frustrates me to see people fight over the "true meaning" where there are, based on the criteria they themselves outline, multiple legitimate stances. I always have this urge to scream "if you kid's don't stop fighting in the back seat, I'm turning this theology round, and we're going right back home!"
Another reason why it bothers me is that the logician in me gets ruffled. I have yet to see someone accuse another of not being a "true Christian" who is not cherry-picking the Bible just as much as the person at whom they are throwing accusations. The Bible is a large, complicated book, and people have been pulling out what they like and ignoring the rest for as long as there has been organized Christianity (and I have to imagine that the same happened with the Jewish peoples before there was a Christianity). So, it really annoys me when I see people hypocritically attack other people for doing the same thing that the attacker is doing.
Quite simply, if a modern Christian wasn't cherry-picking the Bible, they would not be living anything like a modern westerner does. The restrictions and requirements of the religion as laid out in the New Testament simply don't allow for many of the excesses that are a normal part of life in the U.S. and western Europe - and I am talking about things that we all take for granted, such as having enough personal wealth to own a television, a car, a large house, etc. etc. So, when someone accuses another of not being Christian for cherry-picking the Bible, I always want to ask them how that beam in their own eye is doing.
Another aspect of this that sticks in my craw is that it is, quite simply, cheating. If two people are arguing for different positions using the same source material, then it is fair for them to do two things: 1) they can agree to disagree and go on about life, or 2) they can debate and hash it out until they either reach consensus or go back to the first option. So, when someone simply says "well, they're not a real Christian", this is essentially just a cheat, a way of saying "don't confuse me with the facts, my mind is made up!" Essentially, it is the person making the accusation abandoning responsibility for having to defend their position, and then is blaming the other person for the poor behavior of the accuser. It's basically just a form of bullying.
A more practical reason for this to bother me, however, is simply this: it removes social predictability, which is necessary for trust. When someone turns on their own with rage and vitriol over points of religious dispute, I have no way of knowing that they won't turn on anyone else over other matters, especially when the matters over which they are fighting look completely arbitrary to an outsider. Simply put, it makes it difficult to trust someone on other issues when they would rather cast out and attack their brethren who have legitimate disagreements over issues that seem strange or convoluted to an outsider. If someone who generally agrees with them is considered a hated "other", then how will they view someone who has less in common?
In truth, of course, over the years I have found that I can trust some of these folks and that their ire is, for a variety of reasons, directed primarily at their religious fellows. But I have found that my relations with them have always been a bit stressed, as I don't know what will set them off, and as I agree with them on less than those at home they are angry...well, it's a difficult situation to navigate.