Many atheists argue that the existence of an all-powerful, all-good God is not possible due to the existence of evil in the world. The argument goes that it's in the nature of a good being to destroy evil where possible, and that an all-powerful God would find it possible.
I disagree with this because I don't think it is the nature of goodness to wipe out evil. Back in freshman theology, I learned an eye-opening reality -- good and evil are not opposites. That is to say, they are not equal opposing forces which operate roughly the same way. Instead, evil is a lack of good. Good is creative, while evil is destructive. So I can see a good force creating things that are evil, because that good force can't create things that don't lack anything without just creating another version of itself. Evil exists to the degree that there is limitation in created things. And when those evil things are in existence, I could see Goodness not destroying those things because it's not a destructive force, and because all things that are evil contain some good, or they would have no existence at all. Hitler, for instance, had lots of goodness in him -- a healthy body, charisma, rhetorical skill -- and I could imagine a good being letting him live for the sake of those good things.
Beyond this, I don't think that good is simple and easily defined. I dislike Hitler because he murdered humans and I care about humans; but if I had the same sort of love for bacteria, Pasteur would be the bigger mass-murderer. It's impossible for us to think about goodness separate from human morality and human ends, because that is what goodness refers to, when humans speak of it. (And Aquinas, I believe, backs me on this -- morality refers to a being's nature, so good for humans is different from good for God.)
So the problem of evil is kind of a non-problem if you just assume that goodness for God is something about creating and enjoying the universe and not having the sort of moral obligations humans have.
I'd rather talk about what God wants. What are God's goals? It seems obvious to me that if an all-powerful being has a single main goal, he will achieve it. He will arrange the entire universe around that goal. I can do the same with my own life goals -- sacrificing all other considerations to a single goal -- and the only thing that can stop me is my own human limitation. God has no limits, so he will achieve what he wishes.
So: if God's goal were a lack of suffering for humans, he could easily have achieved this. He could do it by being constantly involved, directly stopping any person or thing that was going to cause suffering to anyone. Or he could have made it impossible for the human mind to suffer -- pain, for instance, could be a simple signal of "avoid" rather than including an experience of suffering. Or it could be something that can only happen briefly but vanishes once the message comes across, so that no one could spend days or years in agony. It seems obvious that stopping suffering is no part at all of God's goals, because evolution is a system that relies on death and pain to even work. If you don't want anyone to suffer, it would be stupid to invent a system that requires huge amounts of suffering at every step of the process.
Or his goal could be salvation for everyone. But if it is, the Catholic Church says that God is a failure at it, because there's a place called hell. It seems to me that salvation for everyone ought to be possible. God could have given us only good desires, so we naturally would want to obey God's will. (Such as what the already-saved and good angels experience.) God himself, after all, cannot desire evil, so why can we? God could also carefully arrange things here on earth so that everyone gets exactly the influences that will help them be saved. He could refrain from creating anyone whom he foreknows won't be saved, or let them die before they've had a chance to sin. After all, we know that around half of conceived zygotes die. Perhaps those are the people God knows would go to hell.
But, some argue, salvation for everyone is not God's primary goal either. What he wants even more than salvation for everyone is freedom. He wants everyone to have the maximum amount of freedom possible, so that they could freely choose salvation or damnation. But the world does not seem optimized for freedom either. If maximum freedom was the goal, why are humans limited in knowledge? To make a really free choice, we should see clearly what options are available and what the consequences of our choices will be. The existence of God should be self-evident to everyone, and we should be able to go look at hell so we can see what the danger is. We are not free to choose if we are unable to see what our choices mean until we've already made them all! But that's how it is, if you can't be sure hell exists until you're dead and all opportunity for meritorious choices has ended. I've heard people say that knowledge makes you less free, because no one who saw hell would actually choose it, but that's kind of my point. You are more free when you have more knowledge, because a choice made without knowledge can't be aligned with what you actually want. If you want a lady and not a tiger, knowing which door hides the lady and which hides the tiger is crucial information. Your choices are more predictable when you have information -- no one would actually choose the tiger -- but they are more free.
Also, every human except Adam, Eve, Mary, and Jesus has possessed concupiscence, the innate tendency toward evil. We have disordered desires we can't easily control. It is obvious that we are less free to make good choices when we have concupiscence -- I mean, we all know that Adam and Eve were freer than we are -- but it's also obvious that God could prevent this. After all, the soul is the direct creation of God; it does not come from our parents. Original sin (and presumably concupiscence too) is something on our soul. So for God to make sure each of us gets it, he has to apply it to each soul when he makes it. Why would God do that? Conversely, even if it's on the body, he could easily remove it for each person to increase our freedom.
The third issue is that some people are in situations which severely limit their freedom. Some are deprived of education; others of love. And again, what about the half of humans ever conceived who never make a single choice? If this is a better situation than life on earth, why would God not allow all of us to experience something similar -- creation as an embodied soul and then immediate salvation? But if it's a worse situation, why does God allow it to happen to anyone? It seems to me that the situation of maximum freedom is what the angels are supposed to have: total knowledge, total freedom, and a single choice. And clearly the angels' freedom couldn't be hampered by this, or God wouldn't put them in this situation. But if this is so good, why didn't God let us experience something similar?
I admit that this is a philosophical question and I suck at philosophy. But I've been reading up and I haven't found an answer to this objection. For instance, I read a summary of Plantinga's famous Free Will Defense -- supposed to be the best answer ever devised to the Problem of Evil -- and all it claims to argue is that there could be a potential universe in which there is an omnipotent good God and also evil, not that it is possible in this universe. That's a bit irrelevant, considering we do live in this universe and there are actual facts about this universe we know, like evolution and the death of embryos and freedom that is hampered by circumstances, which seem to complicate the issue. In addition, if you want to profess Christianity rather than only theism, you have to deal with doctrinal complications like hell and concupiscence. Creating a hypothetical universe to do philosophy in is like creating a two-dimensional space to do geometry in -- interesting exercise, but not entirely applicable to the actual world.
It is possible that there are answers to this question. I've been looking for close to a year and not found them. Certainly here on this blog the answers I get usually wind up with "it's a mystery." The argument is that an omnipotent being would be able to come up with a reason why to allow suffering on earth and damnation for eternity, while still caring about humans. I can't accept this, because some of the problems above are not a matter of ignorance, but of actual contradiction.
Now I can posit any number of scenarios that do work out. God could be only interested in creating amazing and beautiful things and observing them, not in the happiness, whether temporal or eternal, of any of his creations. I could still respect a God like this, though of course there would be no point in most of what we call religion. I can also believe in a God who cares and therefore carefully brings all humans to eventual salvation. This is universalism, and the downside is that it's kind of heretical from a Catholic perspective. I've gone round and round with people about it, and I know there are some ways that people manage to be Catholic and universalist, but my conclusion on this is that the only reason a person would ever interpret scripture and tradition that way is because they can't believe in hell and don't want to give up Catholicism -- not because it's a reasonable interpretation of what the Church teaches. I respect the effort, but if you want to be led by the Church rather than to force your own interpretation on its teaches, I think you have to admit the Church teaches people go to hell.
That, of course, casts doubt on Catholicism itself, and on Christianity in general. If statements like "God desires all to be saved" and "wide is the road to perdition and many those who choose it" contain a contradiction with one another, that means that either God can lie, or Scripture is not the word of God, and neither is an acceptable answer.
There are many possible theistic systems which I could accept, which is why I still seek God even though the search gets more discouraging all the time. But I don't feel I have a choice but to reject the doctrine of hell. It is not only morally objectionable to me -- it's actually opposed to reason.