If someone espoused them-self as a health nut when it comes to diet and working-out, etc, and then they ate a pizza with a mtn dew right after they lectured everyone on facebook about how society has become too obese - they are going to get more examination and scrutiny than Bob down the street who just goes about his business and has never taken it upon himself to go public with his diet and how if everyone converted to his diet, the world would be a better place. Even if Bob is over weight and even if the "health nut" guy is right about how people should take care of their body.
Just how it goes.
Same if a guy or gal says swearing is for the uneducated and profane, then go off in a fit of road rage. Even if they don't swear very often.
Same goes for a liberal or conservative politician who gets caught doing something he/she claimed to be against during his campaign and is then branded a hypocrite. Even if they "only did it once".
Same goes for a Ute fan who says byu is a dirty team and is indignant about it but then when a ute player makes a dirty after the whistle, he excuses and justifies it. The masses will come out against this fan in this kind of case (usually on twitter lol).
If there is some truth to it, people will point it out.
Same goes for groups of people, even if most the people are doing what they preach. People will hold individuals/groups up to the standard they tell everyone they have. Might as well get used to it and not worry about it too much since its human nature and EVERY group seems to do it to the groups they are not part of.
In a round about way, this relates to your post.:)