Why do christians ask atheists to prove atheism is real/ prove god doesn't exist?

Don't they understand that atheism means lack of belief in 'god'? So Atheism can only exist after they claimed that something called 'god' exists. Therefore atheism just means not believing in their claim, no? Why do we have to prove that our disbelief in their claim is real? The one making the... show more Don't they understand that atheism means lack of belief in 'god'? So Atheism can only exist after they claimed that something called 'god' exists.
Therefore atheism just means not believing in their claim, no? Why do we have to prove that our disbelief in their claim is real? The one making the claim should take out evidence, no?

If I say invisible men exists, and those who don't believe it are called visism, should they prove visism is real when visism just means not believing in my claim?
If those who don't believe in ridiculous claims made have to prove it false before they can say it doesn't exist, then there can be anything in the world already. Because it's impossible to prove that something non existent doesn't exist.

And even if the logic of 'you can't say god is false unless you prove it' is accepted by people then it also applies to them > 'you can't say god is real unless you prove it' 
Update: Muhammad, lol lots of evidence? If there were lots of evidence, theists would have presented it when we ask for it. Do we even have to do research?
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