Look, here's a proof for the necessary existence of God from the original atheist, Spinoza. I don't care if it makes you believe in God, hell, you can say it doesn't work. What I'm saying is that I'm not intellectually irresponsible for holding this position, because it is rationally defensible.
"The potentiality of non-existence is a negation of power, and contrariwise the potentiality of existence is a power, as is obvious. If, then, that which necessarily exists is nothing but finite beings, such finite beings are more powerful than a being absolutely infinite, which is obviously absurd; therefore, either nothing exists, or else a being absolutely infinite necessarily exists also. Now we exist either in ourselves, or in something else which necessarily exists (see E1A1 and E1P7). Therefore a being absolutely infinite --in other words, God (E1D6) --necessarily exists. Q.E.D."
I couldn't find my better translation of the first sentence, but it reads more easily as "to be able to not exist is weakness; on the other hand, to be able to exist is power, as is self-evident"
You can say you don't agree with the argument, that's fine by me, <i>I'm</i> not even sure I agree with it. But in the framework Spinoza set up, it is logical, and not at all circular.