Beliefs - Atheism VS Theism [Serious]

I have 3 questions for the Atheism community.

1 - How come, every time an Atheist talks about God's non-existence. They always refer to the Christian God? i.e - why the bible is wrong,etc. [when there are so many religions]

2 - Atheist don't believe in a Deity. But would you believe in the existence of a God that doesn't have the personification of a human ? A God that has not been explained by human language. Made of unknown matter[for lack of better words.]

3 - If you don't believe in God + an afterlife. Meaning that - You only live once - this life and that's it. Why do you keep living, why do you care if humanity keeps living, since you won't even know that you were alive at some point?

We could start WW3, who cares, after everyone is dead, no one will remember, right ? If you tell me , you want to teach science so that other generations will learn and so on.. but the final result is always complete non-existence of all.. meaning the universe has no purpose and will also completely disappear. If the final result is always non-existence, why would we care that we exist.

PS : why would killing be bad, if the victim and the killer don't even remember the event in which the killing took place. Both of them won't remember, even the judge, or witnesess won't even remember.

Answer all questions if possible, I am not an Atheist, nor religious. I am a human, meat and bones with a conscious. that is all. You can ask me questions if you want.

I AM NOT TRYING TO CHANGE YOUR BELIEFS. I SIMPLY WHICH TO DISCUSS BECAUSE I SAW THE CREATIONISM VS EVOLUTIONISM VIDEO.

Peace, One love