"How is it not rational to believe in an unseen force that is moral and just ,and that being created all things for his pleasure? "
Oh, I dunno... In the same way that you fundies would say that it's not rational to believe in a mass of durum wheat with pork meat in spherical form, which has antigravitational properties, who lays His Noodly Appendage upon those whom He chooses (those who partake of the blessed sacrament that is Pasta of all kinds, and who Talk Like Pirates on 19th September). Those who, when they die, shall all meet up in the Afterlife, and eternally party around volcanoes that erupt beer, and an assembly line that produces strippers (those who aren't Touched By His Noodly Appendage will meet by a volcano that erupts stale beer, and a factory that produces strippers with Gonnorhoea, Crabs, and the Clap).
Then you'll realise the meaning of this quote:
'I contend that we are both Atheists. I just believe in one fewer god than you do. When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours.'
-Stephen Roberts
...oh, and as for why we Atheists don't go along with your little 'unseen force that is moral and just' (considering the Old Testament):
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Oh, no more please, Mr. Wilde, I am bereft of ribs!
"and that being created all things for his pleasure"
PROTIP: That which is asserted without evidence, can be dismissed without evidence.
And how can something that can't prove it's existence - and an entire insane & unjustifiable mindset based on such, known as 'Faith' - be rational, in any way, shape or form?! You tell me.
Ergo, Atheism. QED. A concept that's infinitely more rational - certainly more than infinitely superior - to so-called 'religion'.