That:If you believe, you have nothing to lose and everything to gain, yet if you don't, you have nothing to gain and everything to lose.
That is
NOT a fact, it is the most stupidest idea supporting the idea of God. That provides no evidence at all that he exists and should not be a reason for someone to believe. If this is you're opinion, and you believe in God for this reason, then you are obviously closed minded and you should believe in anything because
believing in unicorns or fairies has nothing to lose so therefore you should believe in them too.
If you believe in God, it means you have to substitute something away. This God
must have done something, otherwise he isn't God. There are 1000's of different God's to believe in so why would you believe in one over another? In the Christian faith, if you believe that Jesus is the son of God and accepting him as your saviour etc etc, then you go to heaven. Though in the Muslim faith if you believe that Jesus is the son of God you go to hell. Guess that means you are going either way now doesn't it, and with believing in God has just as much potential for loss as not believing.
And God generally goes hand in hand with an afterlife. So if you believe in an afterlife you know, or think, that you are going to live forever in a beautiful place of peace and happiness. This basically makes your life on Earth pointless, so why would there be much of a use caring about it. While someone who doesn't believe know's that this is their one chance, their one life. They have a limited time before going back to nothing and they will make the most of it.
Now if you believe in something like the God of Spinoza, then this doesn't really hold true. If you are under the impression that God created the universe with beauty and simplicity then you will be not so willing to accept things that go against this view. A famous example of this would be with Einstein and he's opinion on Quantum mechanics. He could not accept it because of the randomness and the probability, "I, at any rate, am convinced that He does not throw dice."
As physics and cosmology dwell further into the depths of the universe and closer to how it all began, you will be convinced it is all not true because it goes against your view of a God. You will turn away from the facts and be trapped in your opinion of a world that is completely wrong.
So you see, there is lots to lose, and that argument is purely stupid.