Why do Athiests require 'proof' that God exists?

[Ace Otana]

If tooth fairies don't exist (which is likely) they are ridiculous. However if God exists (which is possible) it is very relevant.

Special pleading. Fallacious argument.
Let me fix what you said....

If tooth fairies exist (which is possible) they are ridiculous. If God exists (which is possible) it is also ridiculous.

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As a member of a religious community (in which the majority are religious) it is the Atheists challenging the status quo, they must justify their beliefs to me.

Why must one justify a lack of belief? You are a theist (one who believes in god) I'm an atheist (which means without belief in god). What is there to justify?

The primary 'reason' you should believe in the possibility that God exists is that there are so many questions unanswered by science.

God of the gaps argument. Another fallacious argument.

Most people believe in the possibility of Aliens existing on other planets - why not include God, Angels and Demons in this belief?

The likely hood of their being other life forms in the universe is huge considering the size of the universe. It's been estimated that there is at least 500 million life capable planets in this galaxy alone. God, angels and all that crap lack evidence, value, credibility and explanatory power. Nuf said.

I'm not saying it proves God exists, but surely it exempts me for the burden of proof.

It doesn't.