John Stackhouse responds to a claim commonly heard from New Atheists, namely, that Christianity is a great source of evil:
Those who would claim the high ground of rational and historical argument ought to sit still for some. And that argument might show–I think it does–that Christianity is not inherently hateful or violent. Instead, it would show that faithful (rather than token or cynical) adherence to Christianity generally makes a measurable positive difference: in terms of the hospitals and schools and science you mention, as well as leading markers of social and psychological health such as lasting, happy marriages, high levels of volunteerism–and, one should note, an ethical structure that actually prizes lasting, happy marriages and high levels of volunteerism.
This is a start at an answer, at least. David Martin’s excellent book Does Christianity Cause War? is worth your reading on this question, as is the volume of essays edited by Kenneth Chase and Alan Jacobs, Must Christianity Be Violent? Reflections on History, Practice, and Theology.