The question of whether or not some sort of god exists is not one which should necessarily occupy the minds of atheists all of the time. Theists — especially Christians — regularly challenge atheists with arguments and ideas which supposedly demonstrate that their god definitely exists. But prior to that, there is an even more important issue to address: is a god really important in our lives? Should atheists even care about the existence of any gods in the first place?
If the existence of a god isn't important, we certainly needn't waste our time debating the issue. It should be expected that theists, and Christians in particular, will quickly say that the question of their god's existence is indeed vitally important. It would not be unusual to find them saying that this question eclipses all other questions which humanity might ask. But the skeptic or nonbeliever should not simply grant them this assumption.
Theists who try to argue that their god is indeed important will naturally support their position by reference to all its supposed characteristics — like perhaps that it offers eternal salvation for humanity. This seems like a reasonable direction to go, but is nevertheless flawed. Of course they think that their god is important, and of course this is closely related to what they think their god is and what it does.
However, if we accept this line of reasoning, then we are accepting a particular set of characteristics which have not yet been established to be true. It must be remembered that we didn't ask if their god with its supposed characteristics is important. Instead we asked if the existence of any god, generally speaking, was important.
These are very different questions, and theists who have never thought about the existence of a god outside of the sort of god they've been taught to believe in may fail to see the distinction. A skeptic might choose later to grant that if a particular god with certain characteristics exists, then that existence could be important; at that point we could move on to see if there are any good reasons to think that this alleged god exists.
On the other hand, we might also just as easily grant that if a particular elf with certain characteristics exists, then that existence would be important. That, however, begs the question of why we are talking about elves in the first place. Are we just bored? Are we practicing our debating skills? In a similar vein, it is justifiable to ask why we are talking about gods in the first place.
Social Order & Morality
One reason which some theists, especially Christians, will offer for thinking that the existence of their god is important is that belief in a god is good for, or even necessary for, social order and moral behavior. For hundreds of years, Christian apologists have argued that without a belief in a god, basic social structures would disintegrate and people would no longer find reason to act morally.
It is a shame that so many Christians (and other theists) continue to employ this argument because it's so bad. The first point which should be made is that it obviously isn't true that their god is required for good social order and moral behavior — most of the cultures in the world have gotten by just fine without their god.
Next is the question of whether or not belief in any god or higher power is required for morality and social stability. There are any number of objections which can be made here, but I will try and cover a few of basic ones. The most obvious thing to point out is that this is nothing but an assertion, and empirical evidence is clearly against it.
An examination of history makes it evident that believers in gods can be very violent, especially when it comes to other groups of believers who follow different gods. Atheists have also been violent — but they have also led very good and moral lives. Thus, there is no apparent correlation between belief in gods and being a good person. As Steven Weinberg noted in his article Designer Universe:
With or without religion, good people can behave well and bad people can do evil; but for good people to do evil — that takes religion.
Another interesting fact to point out is that the claim doesn't actually require any god to really exist. If social stability and morality are only achieved with believing in a god, even a false god, then the theist is claiming that human societies require massive deceit in order to survive. Moreover, the theist is arguing that a society doesn't actually need their god, since any god will apparently do. I'm sure that there are some theists who will quickly agree with this and not be bothered, but they are rare.
A more fundamental objection, however, is the implicit portrayal of humanity which such a claim makes. The unspoken reason why humans need some god to be moral is that they are not capable of creating their own social rules and, hence, require an eternal rule-giver with accompanying eternal rewards and eternal punishments.
How can a theist possibly claim this when even chimpanzees and other primates are clearly capable of creating social rules? The theist is attempting to create ignorant children out of all of us. In their eyes, we are apparently incapable of running our own affairs; worse yet, only the promise of eternal reward and the threat of eternal punishment will keep us in line. Perhaps this is actually true of them, and that would be unfortunate. However, that is not true of any of the atheists I know.
Meaning & Purpose in Life
A common reason used to argue that the existence of a god is relevant to us is that a god is necessary to have purpose or meaning in life. Indeed, it is common to hear Christians assert that atheists cannot possibly have any sort of meaning or purpose to their lives without the Christian god. But is this true? Is some god really a prerequisite for meaning and purpose in one's life?
I honestly don't see how this can be so. In the first place, it can be argued that even if a god did exist, that existence would not provide either meaning or purpose to a person's life. Christians seem to maintain that serving their god's will is what gives them purpose, but I hardly think that this is admirable. Mindless obedience might be praiseworthy in dogs and other domesticated animals, but it certainly isn't of much value in mature adult humans. Moreover, it is debatable whether or not a god which desires such uncritical obedience is worthy of any obedience in the first place.
The idea that this god is supposed to have created us has been used to justify the doctrine of obedience as fulfilling one's purpose in life; however, the proposition that a creator is automatically justified in ordering its creation to do whatever it desires is one which requires support and should not be accepted out of hand. In addition, a good deal of support would be needed to claim that this would serve as an adequate purpose in life.
Of course, all of that assumes that we could clearly discern the will of the alleged creator. Quite a few religions in human history have asserted the existence of a creator-god, yet none of them have managed to find much agreement as to what such a creator-god might want from us humans. Even within religions, there is tremendous diversity of opinion as to the desires of the god being worshipped. It seems that if such a god did exist, it probably wouldn't have done such a poor job as to allow this confusion.
I can draw no other conclusion from this situation than that if some sort of creator-god exists, it is highly unlikely that we'll be able to figure out what it wants of us, if anything at all. The scenario which seems to play out is that people project their own hopes and fears onto whatever god they worship. People who fear and hate modernity project that onto their god and, as a result, find a god which wants them to continue in their fear and hatred. Others are open to change and willing to love others regardless of differences, and thus find in a god which is tolerant of change and variation, and wants them to continue as they are.
Although the latter group is more pleasant to spend time with, their position is not actually any better founded than the former. There is no more reason to think that there is a benevolent and loving creator-god than that there is instead a mean-spirited and fearful creator-god. And, in either case, what that god might want from us — if discoverable — cannot automatically give us purpose in our lives.
On the other hand, it is easily arguable that meaning and purpose in life are ready to find — indeed, create — without the existence of, much less belief in, any sort of god. Meaning and purpose at their heart require valuation, and valuation must begin with the individual. For this reason, they must exist first and foremost in the individual. Others outside of us (including gods) may suggest possible paths for us where meaning and purpose could perhaps develop, but ultimately that will depend upon us.
If the existence of a god is not actually relevant to how we live our lives and certainly isn't necessary to being a good person, then debating the existence of any god may not be too important. You might choose to debate the existence of some particular god in order to pass the time or hone debating skills, but it would appear that one of the more effective response to the oft heard "Why don't you believe in God?" is "Why care about gods in the first place?"
So, could it matter that any gods exist? Maybe, maybe not. Some particular god could matter, depending upon its characteristics and intentions. However, the point which must be recognized here is that it cannot be automatically assumed that any god which exists is necessarily important. It rests entirely with the theist to first explain who and why their god could even matter to us before we use valuable time to decide if it even exists. Although this might initially sound harsh, we are really under no obligation to entertain the idea of something existing when it has no relevance to our lives.