An annoyance I often feel in theism versus atheism debates centers on the fact that atheists frequently do not work hard enough on disproving the gods. I think that the correct approach is to induce total skepticism about the very categories 'gods' and 'existence of gods' every chance you get.
Remember that your aim is not to convince the theist, nor is it to defend yourself (something rarely necessary), but to give your audience permission to free themselves from religious dogma. You will not convert the theist, but you will learn how to argue your position more effectively, and give permission and ammunition to others by arguing in public. So, argue.
You can win the argument over and over again in the minds of your audience no matter what the theist says or does, because disproof can be quite powerful and hard to attack. It can also be easy to remember. It can stick in the heads of your audience until months later. So, always emphasize the disproofs of the gods if you have some.
A very important rule: Never accept the thesis that you cannot prove a negative. If you do that, you cede the territory you should be standing on. Never do it. Of course you can prove a negative. The idea that one cannot prove a negative is a confused one.
The difficulty of proving a negative exists only for empirical/inductive arguments.
There is no such trouble for deductive arguments. To demonstrate this fact, examine the following deductive arguments.
1 Gods are sanctified talking monkeys who live in the sky, but no talking monkey lives in the sky, therefore, there are no gods,
2 Gods are invisible language users, but all language users are visible, therefore, there are no gods.
3 Gods are invisible people, but all people are visible, therefore, there are no gods.
4 Gods are people who can hear the unspoken thoughts of other people, but people cannot hear the unspoken thoughts of other people, therefore, there are no gods.
5 Gods are unlimited in their ability to understand and use the world's languages, but all language users are limited to a relatively few languages, therefore, there are not gods.
6 Gods are immortal, but all living things are mortal, therefore there are no living gods.
7 Everything that exists is natural, and nature cannot make a god, therefore no gods exist.
8 If Christianity is true, there would be people coming back from the dead, but no one comes back from the dead, therefore, Christianity is not true.
9 If gods existed, there would be signs of them, but there are no signs of them, therefore there are no gods.
10 Gods are sanctified persons who live in the sky, but no person lives in the sky, therefore there are no gods.
All of the arguments above are deductive, all of them are such that if their premises are true their conclusion follows necessarily.
An argument can only fail in two ways: either its premises fail to support its conclusion, or it has a false premise. These arguments are valid, meaning that their premises support their conclusions. So, the only defense against any of them is to point out a false premise. That is not easy. When it happens, you must defend your premises.
I like to discuss argument 8 above. Nobody likes the premise that Christian immortality tales directly imply that there would be people coming back from the dead around us. The premise is true nonetheless, because if all of the dead people are still alive and heaven is a free and open society, then they are free to roam the earth. If the dead are not free to roam the earth, then heaven is not a free and open society, meaning that heaven is not heaven, and thus Christianity is false on another front. But because Christian heaven is supposed to be heaven, and therefore free and open, it follows that some of the dead should be roaming the earth. They are not. Therefore, Christianity is wrong about life after death, because if they were right about it, we would see the effects of it, but we do not.
Argument 9 above is essentially a schematic for an argument like 8, because the word "signs" is so vague it could mean almost anything. It helps to put in a specific sign, like argument 8 does. Nonetheless, 9 is useful as stated, because when you are arguing against someone whose world view cancels all value and authority in all other world views, you might as well throw hard balls. And argument 9 is a hard ball across the plate. See if they can hit it. Argument 9 has two premises and a conclusion.
If there were gods, there would be signs of them
There are no signs of them
Therefore, there are no gods
The form here is called Modus Tollens. It is deductively valid, so, its premises fully support its conclusion. The only thing that can go wrong here is a false premise. So examine each. Invite your opposition to examine them.
I believe that lots of people are too shy to talk about what they actually take as signs of a god's existence or agency. Things like having a useful idea at an opportune time, sensing a presence in solitude, or talking to the gods can be hard to articulate and open one up to ridicule. So, do not expect much effort from theists in refuting the second premise. They do not believe it, they think they have the signs, but they are unlikely to publicly recite them. So, their likely move is to try and reject the first premise. They will assert that gods can exist without any signs of their existence. When this occurs, press the meaning question, what does it mean to exist without any sign of it? By sign we just mean effects, any effect is a sign. If I leave footprints, that is an effect of walking, and a sign of it. If I breathe, it disturbs the air around me, and that effect is a sign of my being. Essentially, the theist has just taken the position that a thing can exist without having any effects on other existing things. At this point you can try to chase the theist into the contradiction that a thing can exist without existing, because existence and causation are so close to one another that it is all but inconceivable how a thing can exist without having effects on other things.
If the theist wants a special status for gods, such that gods are the only thing that exists that does not have effects, they have embraced the torturous thought that the most important category of existence is the one that is the most inconsequential.
All of the above arguments are strong, but the strongest are 6 and 7. 6 is the easiest to defend, so let's discuss argument 7 first. It has two premises.
Everything that exists is natural
Nature cannot produce a god
Therefore, no gods exist.
Again, if the premises are true, the conclusion follows with necessity, so, the only way to attack this argument is to falsify one of its premises. The theist probably believes in some way or another that his or her god is supernatural, and that this argument does not touch on such a deity. Their thinking involves a proposition different from the first premise here. They assume that everything that exists is either natural or supernatural. From this they reason that supernatural causation accounts for supernatural things, and natural causation for natural things. Do not help them out by supplying that kind of clarity. Remember, you are not merely arguing for yourself or for the sake of the theist, you are arguing for the freedom of all humanity from superstition based authoritarianism (i.e. religion).
If the theist wants to supply the category 'supernatural' for themselves, start pressing the meaning question. Be sure to say, 'there is no such thing as the supernatural' when the time comes. If they insist there is, demand reasons. If they have no reason for affirming such a thing, then you need no reason for denying it. You have just as many reasons for denying it as they have for affirming it as long as you are both on zero. If they give a reason, then you need one. Also, if you have them on the ropes, and explain that the two of you are equally without reasons for your views, you can then advance your position by giving a reason, and explaining that you have one and they do not, which makes your position much better than theirs. So, it is best to have at least one reason for dismissing the supernatural. The best kind you could give would be one that demonstrates a contradiction in the concept of the supernatural.
Argument 6 is quite strong and almost defends itself. It has two premises.
Gods are immortal
All living things are mortal
Therefore, no gods are living things
If the premises are true, the conclusion follows with necessity, so, the theist has no choice but to reject a premise here. They will not reject the first premise because their god is supposed to be immortal. Their only choice is the second premise. But the second premise is hard to argue with. It is an empirical claim. To disprove it requires an example of a living immortal thing, just as disproving the thesis that all fire hydrants are red requires pointing out just one non-red fire hydrant. If they point to a living thing, it might die tomorrow. It is not immortal yet, in other words. Indeed, every day it has to be checked to see if it is still a candidate for immortality, or if it has died. That goes for their silly god as well as any other entity they might point out. All of them are mere candidates for immortality, and will remain that way for all time. There is no day on which they prove their immortality, because they have to still exist the day after that to count as immortal, and after that, and after that. Assessing the immortality of a thing requires an infinite progression through time. So, the theist will never have their example of an existing thing that is immortal to point at, and so the theist will never be able to falsify the second premise.
Meanwhile the skeptic is happy with his or her knowledge that there can be no credible counter example to the second premise of this argument. And senses that it is almost safe to deem this argument not only valid, but sound.
My point in all of this is to encourage anti-theists to make the effort to argue for universally negative propositions about the gods. There is no such thing, and there can be no such thing as gods. And we can argue quite forcefully for that thesis, and even prove it.
