From a recent Psychological Science:

In Experiment 1, our confederate cheated ostentatiously by finishing a task impossibly quickly and leaving the room with the maximum reward. In line with social-norms theory, participants' level of unethical behavior increased when the confederate was an in-group member, but decreased when the confederate was an out-group member.

So folks will cheat less when they believe outsiders cheat more.  When can this justify preaching that other nations, religions, races, genders, etc. are evil or immoral?