Jesus commands us to love everyone, even our enemies. Hatred, which is the desire for evil to occur to someone, is contrary to this. We as Christians must be careful to monitor our feelings towards others, especially towards our enemies. If we let others' actions bring us to a level of wishing anything bad to happen to them, we commit the sin of hatred, which is a sin against the Fifth Commandment. We separate ourselves from God who requires us to love all.
Although it is at times difficult, we must not allow ourselves to hate, even if it's just one person. In the end, not allowing hatred to enter our hearts will not only benefit the enemy, but also promote peace within us. We need this peace.