I simply say something like: "I'm sorry, but I don't share your faith."
This way you
1.) avoid going on the offensive,
2.) you deflect from an argument about the existence or nonexistence of a god to the subject of their faith, which is more discussable, and makes them consider what they believe rather than attacking what they thinkyou believe.
3.) usually end the discussion if that is what you want.
I have several points. First of all I tell them that there are hundreds of belief systems with millions of deities and they are all claiming to be simultaneously correct. Then I say that if there was a one true god and a one true belief then we would all come into the world knowing it. Then I say that these religions were all developed at a time when everybody knew that the flat earth was the center of the universe. Then I go get a sandwich.
Defense of atheism often comes out as attack on religion, so a persuasive argument to me (nothing is really persuasive to the religious, is it?) is to describe the bible as written thousands of years ago by primitive superstitious people dealing primarily with things of interest only to themselves.
I would usually say something like, Extraordinary claims require extraordinary proof. So personal experiences won't do. To back it up I would say: That if you tell me that there is a tree in your backyard then I will believe you, then your personal evidence is acceptable because having a tree in your backyard is ordinary. On the other hand if you tell me that there is a tree that walks around then I will not believe personal experience because the claim is not ordinary. I will not buy personal testimony's because they might be illusions.Now I require other proof like pictures or videos and other things that is irrefutable. They same thing goes with God.
Another point that I often make is, How do you know that everything was created?
Then they will say something like, but everything must be created otherwise where did it come from? Then I reply:"That everything does not need to be created but everything needs to have an explanation. And by saying that its God/Creation you are asserting an explanation without proof.
And an explanation is only acceptable if it has proof and can be tested."
I would also usually ask, How do you know everything was created? And that creator was God?
And they just rephrase the question and answer: Everything must be created. How did it get here then? Look at the trees. How are they here? They must ne created.
And I reply: Everything must have an explanation. It need not be created. By saying that everything is created you are asserting an explanation without proof. And an explanation is only acceptable it has proof and can be tested. Also you did not answer my first question, How do you know that everything was created? Do you have supernatural powers that I don't have?
How was everything created or why is there everything instead of nothing is a really good question, I seek that answer myself. Probably never will have it answered though. How was God created is also a good question. It is just as mysterious and it puts them in the same predicament as you during that discussion.
The term "defend my atheism" is open to a broad interpretation. Answers from any interpretation are welcome.
Our justice system is in no way perfect. It needs a total revision in my opinion. The minor crimes criminals go to "school" (prison) and learn to be hardened criminals. I believe the punishment should fit the crime totally. To cut off someones hand because they stole an apple is total nonsense. That person has to "do the time" for the rest of their life. It only builds distrust and grudge against the government. Separating the people from the government isnt a progressive system. So yeah, I agree.
I usually ask them to clarify. Of 200 billion stars in our galaxy and an equal number of galaxies in the universe, an infinite, all powerful entity that just popped out of nowhere picks our ball of dirt to do its magic on. Then after it has created everything, in 7 days no less, the god only appears to a nomadic and illiterate group of goat herders and gives them a bunch of confusing and convoluted rules to live by (which they have to memorize because they are illiterate). And, if they violate those rules punishes them with death and destruction. Then the god gets so pissed with the humans it created it drowns all but a handful of them.
Is that the god you are talking about? And, if not, which one are you referring to?