You can also look at how much harm atheist regimes have caused. With Christianity you forgot how the early Christians were persecuted simply for their faith, and you do not bother to look at the news today at how Christians around the world are being persecuted for their faith.
You can only say all religions are man-made if you do not believe in God at all. Otherwise there is at least one true belief. For me it is Christiainity. In Christianity it is not man counting himself worthy of salvation, or earning his salvation. It is man realizing that God himself has made a way for salvation, and that it is a gift from God, and that God is love. This erases man's ability to consider himself better than the next person, and for a lot of people this is an unacceptable thought.
Remember the Christian is the one who follows God out of love and gratitude. Your torturers would be considered otherwise.
It is PEOPLE have caused the harm, not Christianity. People are hypocrites and want power, and want control over other people and like to force their will on others. If these people choose to be hypocrites and commit atrocious acts, then that is NOT the fault of Christianity. It does not make Christianity any less true.
Let me ask you a question : If your algebra teacher was a child molester and a murderer, does that make algebra any less true?
Because I know the actual history as opposed to the thing you have been taught in its place. Read the accounts of the first and second century Christians, see how much torture they committed. Read of the monks and the monastic movement or the ascetics.
That's only because people do not practice the true meaning of their religion. The same could be said for Islam. Both Christianity and Islam support peace, people just carry it out wrong. That's just human nature, nothing to blame on the religion, it's just an excuse they use for their actions. But read the Bible or the Quran and you wont see such violence.
That's just like asking, "How can you live in the south, when they had African-American slaves?"
Just because a religion (or geographic area) has been responsible for suffering of others in the past doesn't mean that it is now. So your point is moot.