Vices are sometimes only virtues carried to excess!--Charles Dickens
One of the many things that motivates the horrific mob behavior of the religious is a human tendency to compete with each other for status within our group. Once the group decides that a certain behavior or attitude is a virtue, group members will start to compete with each other over who best exemplifies this attribute.
The religious are particularly prone to this behavior because of the extent to which they are motivated by conformity, egotism, and narcissism. Religion is so intertwined with the egos of the religious that they will compulsively engage in this sort of competitiveness with regard to it and its precepts. This "holier than thou" behavior will inevitably start to spiral out of control because their world view is based on the idea that they are followers of the ultimate being. There is no outside influence that can temper this competition because all other influences are considered to be far less important.
The result is that, in their attempt to be the most virtuous, the religious continually outdo each other until they pass the point of diminishing returns for their virtuous behavior and then pass the point of any returns for their behavior and the behavior itself becomes more harmful than the evil the virtue was meant to remedy.
For example: Gluttony is a sin? Well, then don't be a glutton. Everyone else is trying to deny themselves extra food, too? So much so that you can't stand out from the crowd and show everyone how virtuous you are? Well, then, obviously it is time to starve yourself until your emaciated frame proves to everyone who sees you that you are completely unconcerned with the needs of the flesh. Your cadaverous appearance shows everyone that you care only for the next life. Skip a few more meals and you'll get there!
Pleasure is wrong? Celibacy isn't sufficient proof of the fact that you are more virtuous than everyone else? Well, how about a little self-flagellation? That ought to prove just how little you want pleasure.
These two examples illustrate this phenomenon very well because they seem to appear in almost every, if not every, religion with a large number of adherents. Even religions that are as different from each other as Catholicism and Buddhism provide ample examples (no pun intended) of this type of behavior.
Why should anyone care if some zealots starve and flagellate themselves? Because, unfortunately, people don't simply compete through individual performance. They also compete by trying to tear the competition down, sometimes using methods that are unethical, unkind, and unfair.
Combining that tendency with the fact that many of these "sins" that the religious seek to avoid are simply side effects of being human (such as a desire for plenty to eat and a satisfying sexual relationship) can have some rather nasty and unfair results. So nasty and unfair that they outweigh any harm caused by the "sin" that the "competition" is accused of. People can lose their reputations, their jobs, their families and even their lives when this sort of competition rears its ugly head.
When I wrote that churches are simply "standing lynch mobs", I wasn't speaking entirely metaphorically. They are often ready not only to pounce on the alleged enemy of one of their members, they will quite readily pounce on one of their own. One might be tempted to think that this is some sort of twisted practice, but in reality it is the nature of the system religion creates. That system is one of sometimes vicious competition to be "holier than thou" in a "moral" system that declares virtually everyone to be immoral simply because they are human and which makes more than frequent use of the natural moral instinct to punish the wicked.
Every church member is the church's potential next mobbing victim because they are all guilty simply for being human. So, how is the victim chosen? Well, the same way mobbing victims have always been chosen: by being unpopular with the wrong people.