Religions have many problems, but one of the biggest issues which religious people have constantly to deal with is that of dealing with "The Crazies". One is constantly hearing people of various religious beliefs making statements such as, "Well, they're extreme. I'm not like that." How can a religious person deal with these extremists and still have a religious identity? It's hard. Muslims in many countries are very non-violent, however Islam is still viewed as a very violent religion by many people. Christian Fundamentalism is considered an extreme by many Christians, yet when a person identifies as "Baptist", it still brings with it thoughts of dancing with snakes and miracle healings.
One of the problems with religions such as Islam is that there are extremists, such as terrorists, who also claim to be devout Muslim, and yet many Muslims do not want to be associated with them. It's hard for a Muslim to separate their religious views from those of terrorists because, well, they originate from the same holy book. As a matter of fact, the Koran even has statements which clearly say that a devout Muslim should kill "infidels". (Yes, it also has statements about caring for everyone, but it's not clear if the "everyone" in those statements is really talking about non-Muslims. In general, non-Muslims are thought to be the equivalent of non-human, so killing them is no big deal. This is stated in the Koran as well.)
Christian Fundamentalists are well known for their extreme views, such as claiming to handle wild snakes without being bitten, claims of miracle cures, claims of "speaking in tongues", even "Young Earth Creationism", and literal interpretation of the Old Testament. While most main stream Christians do not associate with these beliefs, they are an integral part of many aspects of the religion. It can be embarrassing to have to admit to being "Christian" because of the close association of these ideas.
I would maintain that "The Crazies" will exist in pretty much all religions and I'll explain why. Religious ideas are based on nothing but a single person's interpretation of what they have read, heard, or learned from others. When "God speaks to you", it can clearly be demonstrated that this amounts to little more than your conscience talking to you. (Isn't it interesting that "God" always likes the same people you like and hates the same people you hate?) Even though most religions have a "Holy Book" of some type, this book was always written by someone quite a long time ago who thought differently from us today, due to societal changes. Thus, the "Holy Book" must always be interpreted by the reader. Some make this interpretation in as literal of a fashion as possible, but we all know that if you literally followed the Old Testament rules, you would end up in jail very quickly! (Leviticus 20:9 and many others) So, interpretation is always there, no matter how "literal" a person feels they are taking the text.
Since interpretation is always there, then ultimately the understanding of any religion is always inside the head of the individual. If religion were more like Science, then a person could appeal to facts and evidence to back up and to "ground" their understanding. Since religion really does not have any such grounding, then every idea which is part of every religion is ultimately a matter of opinion! That explains why there are so many! There are many people in the world with many different life experiences and backgrounds. Thus, everyone's opinion will be slightly, if not completely, different. This can not really be avoided and religion has no grounding in anything which can be demonstrated in the real world, religion will always be "all over the map" with interpretations.
So, sorry to say, "The Crazies" will always be part of any religious belief system, since there is no grounding in the real world. I guess religious people will just have to continue to fight for their own beliefs and as we have more people in the world, we will also have more religions!