This is a classic smokescreen question often asked to avoid having to grapple with the evidence for authentic Christianity. At best, it involves a hasty generalization. At worst, it’s a way of “poisoning the well.”
To begin with, this question was anticipated by Christ, who long ago proclaimed that his followers would be recognized by the way they lived their lives (John 15:8). Thus to classify as Christian those who are responsible for instigating atrocities, is to beg the question of who Christ’s disciples are to begin with. As Jesus pointed out, not everyone who calls him “Lord” is the real deal (Matthew 7:21–23).
Furthermore, this question implies that Christianity must be false on the basis that atrocities have been committed in Christ’s name. There is no reason, however, why we can’t turn the argument around and claim that Christianity must be true because so much good has been done in the name of Christ. Think of the countless hospitals, schools, universities, and relief programs that have been instituted as a direct result of people who have the sacred name of Christ upon their lips.
Finally, those who use this argument fail to realize that the validity of Christianity does not rest on sinful men but rather on the perfection of Jesus Christ alone (Hebrews 7:26; 1 Peter 2:22). Moreover, the fact that professing Christians commit sins only serves to prove the premise of Christianity—namely, “all have sinned and fall short of the glory of God” (Romans 3:23); thus all are in need of a Savior (1 John 3:4–5).
For further study, see R. C. Sproul, Reason to Believe (Grand Rapids: Zondervan, 1982); Lee Strobel, The Case for Faith (Grand Rapids: Zondervan, 2000), chapters 4 and 7.
“Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but only he who does the will of my Father who is in heaven. Many will say to me on that day, ‘Lord, Lord, did we not prophesy in your name, and in your name drive out demons and perform many miracles?’ Then I will tell them plainly, ‘I never knew you. Away from me you evildoers!’”