The worst thing about Christianity is real and fake Christians that are hypocrites. Those folks, myself included to some extent, have done some dastardly deeds of evil.
There are some really nice, kind atheists out there. And there are some nasty "Christians." We've probably each met some of both. And certainly, from my perspective, those who claim to be followers of Christ and His Word will be held to a higher standard.
However, it has become popular to decry the "dangers of institutionalized religion" and talk as if religion, especially Christianity, is the sum of all evil. The assumption therein is that it is the objective atheists who hold the answer to peace and harmony.
Here's the historical fact as far as I can tell: the worst of what Christians have done cannot compare with evils of institutionalized atheism, and the blessings of the Church on societies around the globe cannot be overshadowed by any other movement, especially atheism.
Consider just this: The Black Book of Communism: Crimes, Terror, Repression (click here for a review), published by Harvard University, reports the death toll at the hands of communist (atheist by definition) institutions to be around 100 million people. That is almost inconceivable. Perhaps it is atheism that we ought to find dangerous...