Glass houses

We've heard it a dozens times before, the "people living in glass houses shouldn't throw stones" or "pot calling the kettle black." This is used by people who are for the most part, clueless and used to justify their own bad behavior.  It doesn't address the problem. 

Just pointing out that the accuser is guilty of something doesn't mean that you are innocent of it. IE-swearing. I've seen people say "Hey, I've heard you curse. Why do you say that others shouldn't?" Just because you have a bad habit doesn't mean you endorse the behavior in others. I've also heard people say "You were divorced. How dare you say I shouldn't be!"Again, just because you have done things in your past that aren't the greatest doesn't mean that someone should follow your own lead. Not only that, but circumstances change and no one knows the entire story. 

People say "pot calling kettle" to try and show that you aren't perfect either. It's their way of absolving themselves. These are people who generally lack the ability of self critique and in therefore, they think they are more moral than the rest of us. Those who think they are the most moral are almost always without question the least.