Atheism is not a philosophy. Atheism is the disbelief in the proposition that a God exists. The statement is given by a theist: God exists. The answer is given by the atheist: I don’t believe that statement. That is all atheism is. It is not a philosophy in itself. It is not a worldview. It is simply saying that one doesn’t believe the proposition that a God exists, nothing more. Let me put it this way: everyone is sitting around a dinner table. Some people are eating chicken. Some people are eating pie. Some people are eating burgers. I am not eating. That is atheism. It makes no sense to then ask me what I am eating. I am not.
People often get confused because they present their arguments for the existence of God, and when an atheist rebukes those arguments, they think it is because the atheist has some worldview which lies behind this rebuttal. But the atheist does not. The atheist rejects the arguments because the arguments do not make sense. This rejection does not depend on the atheist having any worldview. The atheist is free to reject the arguments in favour of the existence of a God whether the atheist is also a communist, or a capitalist, left wing or right wing.
Atheism is often confused with Humanism. From humanists.uk: “(a humanist) believes that, in the absence of an afterlife and any discernible purpose to the universe, human beings can act to give their own lives meaning by seeking happiness in this life and helping others to do the same.” This is a philosophy. An atheist, however, is free to be a humanist or not. It is not necessary to have any philosophy in order to reject the claims of another. I do not have to be eating anything in order to refuse a plate of prawns.
Many atheists are not interested in debating religion at all. Many atheists are. Some of the atheists who are interested in debating the question of the existence of God are also anti-theists. This means they believe theism is a something negative. This is a philosophy. An atheist is free to be an anti-theist or not. Many are. Many are not.
Crucially, an atheist does not make the claim that a God does not exist. That claim would need to be proven. Making that claim is a different matter from rejecting the claim of another. The atheist is not in the business of disproving something which they do not believe to be true.
The burden of proof is always on the person making the claim, so if you tell me that you are keeping dodos in your garden, it is not up to me to prove that you are not. It is up to you to prove that you are. And until you can do so, I am entitled to say that I don’t believe you. My decision to not believe you may be right, or wrong, but since dodos are extinct, I decide not to believe you. If you bring me to your garden and show me the dodos, I will believe you. However, if you say that your proof is that without these dodos, how do I explain the scratch-marks on the wall outside your house, I will still not believe you because there are many explanations for scratch-marks which do not involve resurrecting extinct animals: this is Occam’s Razor: the simplest explanation is usually the correct one. Might I be wrong? Sure. Might you actually have brought the dodo back and be keeping some in your garden? Sure. But until you can present me with some better evidence than a few scratch-marks, I don’t believe you.
Let’s take it a step further. Let’s say you now tell me that these dodos are the source of your sense of morality. They inform your life decisions. They make you happy. They created the universe. Well, none of that matters because you haven’t shown me that they actually exist. It doesn’t matter how many extra attributes you pile on top of these dodos, if you haven’t proven that they exist, I still don’t believe you.
Then there is the argument that an atheist has to prove how the universe was created. If it wasn’t the dodos, then who was it? That’s the argument from ignorance. Just because I don’t know the answer, doesn’t mean it was your dodos who created the universe. And where do we get our morals if not from these dodos? Again, just because I don’t know, doesn’t mean it was your dodos. Incidentally, there is an abundance of research which shows how we get our morals; the existence of a God is not necessary in this consideration.
The list of arguments which have been presented for the existence of any gods goes on and on. There have been volumes written about these arguments. Some are better than others, but none of them have so far proven the existence of any god. An atheist is under no obligation to be open-minded, but you will find that most of them are, and while they are not eating, they are free to listen to others talking about their meals – and to refuse to eat.