I think people brought up as JWs have a holier than thou attitude. They are constantly told they are the only ones that god has chosen and that God doesn't even listen to the prayers of anyone else. This us vs. them mentality makes a person feel superior, But it also creates a mental need to find the bad points in everyone outside their religion to justify keeping them at a distance and their eventual destruction. It is part of cognitive dissonance.
How many of us really wanted 99.9% of the people on earth slaughtered by God? The only way to protect yourself is to demonize these people in some way. It is a constant struggle to justify why your loving God is going to kill your father, sister, aunt, cousin, workmate, neighbor, etc., when you can't see the need for it. So you try not to think about it and constantly look for the bad in people.
Does this carry over when you leave. Yes, but for the first time you have a chance to realize what you are doing and why. That is the first step in starting to change how you react to others. It won't change easily or quickly, but it is worth the effort you put forth. If you gain just one true friend and treat others more gently and less judgmentally, you will be much more in line with the example of Jesus.