There's no conclusive scientific evidence that there is a god, of any kind. Therefore, believing in one is irrational. Plus we also don't need a god to explain anything in this world. Physical reality would work exactly the same way as it does now, without one. And the simplest, most obvious explanation, then..? Is that there isn't one. Occam's razor, and all that.
Plus also..? Biology and cosmology explain our origins, and how this universe came to be. There's no need for a god. But we know why people came up with gods. Because they were trying to understand and explain phenomena they did not understand, at the time. So they invented complex mythologies. Which, today..? We no longer need that stuff. Plus many religions make mutually incompatible claims, that cannot all be true at the same time. But still..? They can definitely all be false! Which is the most reasonable conclusion to arrive at. And.. we can also see how different religions have developed, and affected each other, throughout history.
Another great argument for atheism, other than the obvious lack of evidence..? Would be the problem of evil. Nature is cruel. The universe doesn't care about us. Really bad sh*t happens to good people! What kind of fair, good, just god could possibly allow that..? Much more logical that it's all just a matter of chance.
We've got such a MUCH better understanding of our own situation, and why we're here, these days! Due to the advents of science... But with the stuff we do NOT yet understand..? That doesn't automatically mean "God did it!" God of the gaps is still NOT a valid argument! And we've just simply got to work on finding the real answers…
There are many psychological factors that can explain god belief. And it makes sense that people would feel the need for sort of an extended, divine parental figure, when sh*t gets tough… Probably it's the same dynamic at work there as what people feel with their real, biological parents! Just that our brains, fallible and biased as they are, transfer that need for emotional support onto this externalized concept of a "God", that of course does not really exist… But it's still got psychological benefits! Hence why people still believe in it! Plus also, religion and god belief probably developed as a way of promoting closer communities… It's kept people together as a tribe! And it's very much founded in our varying cultures… Which is why it's still being passed on to this day, even though there's zero evidence for it.
..There you go. A bit rusty, perhaps. I haven't done this in many years now! But I think I did okay, no..? ;)
PS: it was fun!! :D
Former atheist. Stopped being one in early 2012. :)