The most common Christian theology is that God is infinitely merciful and just. This is repeated over and over like a mantra.
Of course being merciful and just doesn't mean that bad people should never be punished. However, it does mean that the punishment should be humane and uncruel. There's a reason why things like torture and unusual punishment are considered to be against basic human rights and morals. Punishing people for their crimes does not mean that they should be made to suffer needlessly.
When you read how God behaves in the Bible, it paints a rather different picture from an "infinitely merciful God." And I'm not talking just about eternal torture in Hell. I'm referring to how God punishes living people in the Bible's stories.
Noah's flood is really ubiquitous to the Christian theology. It's really prevalent and something found everywhere, from serious theological papers to children's books. That's right, children's books. Basically no Christian seems to even try to think what kind of story it is.
So humanity had become completely corrupt and wicked, and God wanted to destroy them all. How does the infinitely merciful and just God does this? Does he, for example, make them just disappear? (After all, if God is all-powerful, that shouldn't be any problem at all.) Or maybe just make them suddenly die and that's it? No, he decides to flood everything.
Flooding is a huge catastrophe that causes enormous amount of destruction and suffering. There's probably no need to point out the news footage from recent tsumanis in order to get a good picture of what it looks like. It's a horrible, horrible way of making people, adults, children, everybody, die in agony and suffering. And this is being told in children's books.
Or what about Sodoma and Gomorra? God wanted to punish these cities for their corruption and wickedness, so what does the infinitely merciful and just God do? He makes fire rain from the skies. This is ostensibly even worse than flooding them.
Do these and other similar acts sound like the behavior of an infinitely merciful and just ruler? Or do they sound like the behavior of a cruel and power-hungry dictator who has no qualms in making his subjects suffer horrible and agonizing deaths because he doesn't like them, even though he could perfectly well treat them in a more humane way?
What exactly is the claim of infinite mercy and justice based on? Not on the Bible stories, that's for sure.