This is so very true. Often during times of war, one nation will come up with a derogatory name for the other nation's troops. This dehumanization can make it easier for soldiers to kill their enemy.
What I find ironic about Jehovah's Witnesses is that back in the 1990s there was a Watchtower Study Article dealing with this. The article commented how the Pharisees of Jesus time referred to their fellow Israelite as "People of the Earth" which followed the same connotation as "pagan" or "heathen". These were slurs aimed at people who were thought of as uneducated and the last to convert to the state religion.
The point the article made was that Witnesses should not refer to non-Witnesses with derogatory terms as "worldly". The problem with this, even though they were correct, if that using the slur "worldly" is so ingrained in Witness culture it never really caught on. As someone pointed out in another thread, one of the reasons it is so hard for Witnesses to leave is because the whole concept of being a Witness is that it makes you better than all other people. No matter a person's wealth, power, or stature in society - being one of Jehovah's Witnesses automatically makes you better.