Christianity played an important role in the development of Western civilization. I'm not sure any atheist would dispute that. What this atheist isn't so sure about is the commonly heard claim that Christianity is largely a positive force in the world today. Even if one wanted to acknowledge that Christianity was mostly a good thing in the past (and I would have a difficult time doing so), that says little about whether Christianity is currently a good thing. That is, it could be the case that Christianity helped us get to where we are but is now holding us back in important ways.
Atheism does not entail opposition to Christianity or any other religion. Some atheists find great value in some religions, even while suspecting that religious believers are wrong about their gods. For those of us who do oppose religion, this sentiment often comes from our suspicion that various religions are doing more harm than good. Human rights, limiting scientific progress, and theocratic strivings are just a few examples to which many atheists will point.
To be clear, it isn't that we think the world would be some sort of utopian paradise if religion disappeared tomorrow. Most of us recognize that we'd still have plenty of challenges. We might even find ourselves confronting some new ones. But many of us believe that a world without religion would have fewer barriers to progress and would be a step closer to reality. By living in accordance with reality vs. fantasy, we just might be better equipped to solve the many problems we face.
"But why do you care so much what individual religious believers believe?" Religion is made up of people, and so what individual religious believers believe matters. It matters far less than how they behave, but it is still relevant. A Christian who is adamantly opposed to reproductive rights does not exist in a vacuum but is someone who may be taking active steps to limit others' rights. That makes what they believe relevant. And since bringing about desired change often hinges on the political process, the religious values voters who vote their religious beliefs also make their religious beliefs relevant.
I'm sure there are plenty of people who identify themselves as religious believers (e.g., Christians) who believe relatively little religious dogma and whose behavior is not particularly influenced by any of it. I'd agree that what they believe (or claim to believe) is far less relevant. But even here, their expressed support for a religious tradition helps to maintain the religious tradition. And so even here, it would be difficult to claim that what they believe is entirely irrelevant.
Do Christianity and other religions contribute any good in our modern world? I believe so. At least, I believe that many Christians and other religious believers do good in the world which they attribute to their religious beliefs. Religious institutions, if nothing else, help to organize and direct at least some of these positive actions. So no, I wouldn't claim that religion is 100% evil or useless. This is part of why I would not expect that we would see nothing but improvement in every area if religion suddenly disappeared from the world. But on balance, I do think we'd probably be better off. It would take us some time and effort to get there, but I do think we'd be better off.
