One answer would be to point out all the good that has been done in the world by people who took their faith in God seriously. Committed Christians have always tried to put into action the Bible's command to "Love your neighbor as yourself" (Leviticus 19:18).
From the civil rights movement to the establishment of thousands of hospitals and schools across the world, men and women who took God seriously have made an impact for good. When a humanitarian crisis hits anywhere in the world today, Christian organizations are often the first to respond. Where would our society be if all the church-based programs that reach out to those in need suddenly came to an end?
Yes, people have sometimes twisted God's truth and done great evil–but when they have, they were ignoring God's clear teaching. When Peter reacted with violence as Jesus was being arrested, Jesus rebuked him: "Put your sword back in its place ... for all who draw the sword will die by the sword" (Matthew 26:52).
The real problem, however, is the human heart. Down inside, we are selfish and want only our own way–and this causes conflict. And this is why we need Christ, for only He can change our hearts and replace our selfishness with His love. Have you asked Him to come into your life and change you from within?