The difference is that while bad things were done in defence of Christianity, I can think of any amount of positive accomplishments in the name of Christ; can you think of anything positive that was accomplished in the name of atheism?
So when a Christian does good deeds, that's "in the name of Christ", but when an atheist does good deeds, that's by your definition never in the name of atheism? Has it occurred to you that most atheists aren't interested in doing things "in the name of atheism"?
Have you ever considered the possibility that atheists do good deeds because they think that it is the right thing to do, and not something that they need to do in order to "validate" their atheism?
And you can substitute "atheism" for any other -ism or belief or religion or tendency you can think of. The same principle applies: just because you center your entire belief system around a religion and try to "validate" it in certain ways, does not follow that everyone else behaves the same way or thinks they have something to prove in this regard.
I'm not an atheist myself, but I always am amused by those who set out to "prove" that only theists can be moral, good, rational, or what have you. It's a profoundly blinkered point of view, and does not help the public image of Christians or other theists who argue that way. It makes them look rather silly, in fact, to those who have eyes to see how real people - atheists and Christians alike - actually behave. Most atheists aren't leftist Marxist totalitarians, just as most theists aren't fundamentalist religious terrorists.
I knew I should not have clicked on this thread. This is a topic that sheds more heat than light; just igore me. I shouldn't have come in in the middle of this conversation.
I never said that an atheist cannot be good or moral. I know that others say that, -- I did not. I do think that a religion impulse is the foundation of any morals, but I would not say that atheists necessarily lack morals -- or that all theists are moral. That is because religious instinct may or may not be recognized as such.
When an atheist does a good deed he does it because he knows from some source that it is good. But atheism cannot be that source, because it does not say anything positive, it is an absence of a concept rather than a concept. For example, many atheists died in WWII. But they did not die saying: - "Because God does not exist I will risk my life liberating Europe". They said, - "Because liberating Europe is good I will risk my life doing so". Atheism is irrelevant to their heroism. Many Russian soldiers were atheists and did heroic things, but they did them in the name of they motherland, or their leader, or to avenge suffering of others, -- all positive reasons. Atheism is not a reason to do anything.
A Christian, on the other hand, can say - "Christ taught me to sacrifice my life for others, so I go to war".