Have your characters been brought up to hate others (think Romeo and Juliet here)? Do they accept this or query it? What happens to those who don't toe the line? How would prejudices against a group change when your character has experience of being with that group and discovers all is not as he/she had been informed? One of my favourite things from The Lord of the Rings is the way the elf, Legolas, and the dwarf, Gimli, learn to actually like each other from being totally prejudiced against each other (the elf and dwarf hostilities go back a very long way in fiction) at the start.
Do you have characters who find it difficult to relate to others? Are they psychopatic or just selfish or just not used to having to get along with others? Do they change and, especially if not, how to the other characters handle them?