Wrong. Atheism is the refusal to accept claims of existence of deities. Atheists do not claim nonexistence. Atheists refuse claims of existence. These are two different things.

Atheism is also lazyness. Instead of spending thousands of words explaining that all definitions of deities are invalid scientifically and/or philosophically, instead of explaining that the doubt of agnosticism can only make sense after a definition of deity which makes sense... well... we simply throw 4 words: deities do not exist.

We atheists do not really *believe* that the Universe came from nothing. First of all, you need to understand what *nothing* means in Theoretical Physics. It's not what you think.

Long story short, you (as a religious person) may either *believe* that the Universe came from nothing or you may believe that the Universe came from something magic which, in turn, came from nothing.

You may tell me... hey! God always existed!
Well... if your head can accept things that always existed... in this case... you can accept that the Universe always existed.

The difference between the Universe and the "something magic" you believe is that the Universe is here for us to see, touch and experience, whilst your "something magic"... well... is not more than wishful thinking.