To demonstrate why I reject religion, I am going to talk about one example: the story of Noah and the Flood.
In that story God floods the Earth and kills all people except Noah and his family. The flood presumably also kills all the land animals except the ones Noah takes in his Ark.
This story is almost celebrated. There are cute pictures of the ark and animals for kids and there are even children's books based on it. It might seem cute until you consider the death and destruction which is conveniently ignored. It's actually like having cute pictures showing how wonderful the Holocaust was.
Supposedly all of the people that got killed were wicked. That's hard to believe. Does it mean even children and newborns were evil? What about the whole killing aspect? Most people seem to be okay with punishing evil, but did they all really deserve the death penalty? Oh, and what about the animals? Drowning animals is cruelty. Why did they deserve it? Surely an omnipotent being can be more selective in its wrath.
Then there's the impossibility of the whole thing. Consider all the species of land animals, the way some only live in remote regions, and the way some require very specific food. Consider how many employees a zoo needs, and many more animals the ark would have. Okay, that could be resolved with divine assistance. A more serious problem is that a global flood would leave some unmistakable traces for geologists and archaeologists. I don't mean what some say are traces, because those couldn't possibly be from such a recent flood and they're not worldwide. The Bible didn't say anything about God hiding the evidence.
After the flood, God said he wouldn't do it again, which may seem nice, except that he's apparently still free to hurt people and end the world in any other way. For an example, read Revelations.
If it seemed like the flood happened, I might conclude that God was messing with people as evolutionary algorithms. However, considering the lack of evidence that it happened there is one very satisfying answer: it's fiction and metaphor.