When it comes to belief in a perfect creator, one has to inevitably answer the question of "why, then, is there evil?"
To summarize, Epicurus is claimed to have said: "Is God willing to prevent evil, but not able? Then he is not omnipotent. Is he able, but not willing? Then he is malevolent. Is he both able and willing? Then whence cometh evil? Is he neither able nor willing? Then why call him God?"
That quote, alone, will leave many "believers" with little to say. We must, however, go a bit further - expand on the claims of the "believer" to show that what they claim to believe is, well, hardly thought out.
Most often it is claimed that evil comes from "free will" - something that is "god given". Humans have the ability to make their own choices and it is through this that evil is created. The "necessity" of "free will" is never really explained - why must we have free will if the ultimate consequences appear to be far worse than any potential benefits?
Free will, it is argued, provides the ability for empathy through our own suffering, courage through our own situations of danger/fear and happiness from our own periods of sadness. The arguments are weak and fail to mention "natural evil" - why does "god" allow (cause?) earthquakes, tornadoes, hurricanes, mudslides, plagues, viruses, disease, cancers (the list goes on)?
We have to remember (at least for the Abrahamic religions) that "god" supposedly had created a "good" world - prior to (let's ignore the misogyny for this posting) Eve eating the forbidden fruit. We must consider, though, what is promised by this "loving" "god" - heaven.
Heaven is not well defined - when you ask a Christian what heaven is, you are almost certainly not going to receive a standard response. To each Christian, it seems, heaven has its own meaning. Some universal claims about heaven include "eternity", "eternal happiness", "joy", "peace", "no sickness", etc. The bible, itself, refers to peaceful conditions on a new earth and bodily perfection (no hunger, illness, thirst, death, etc.).
If we accept the idea (for the sake of discussion) that heaven is an ideal place - with no suffering and eternal happiness, the question that "believers" would have to answer is "why did god have to create anything less on earth?" If free will isn't necessary for eternal happiness in heaven, it wasn't necessary on earth. If humans could live forever in heaven, why couldn't they do so on earth?
(Never mind the question of at what stage in development we'd be in heaven (what age, what shape, etc.) Do people who die at 15 live in heaven as 15 year olds? If that is the case, wouldn't they all rather die young? What about a baby who dies shortly after baptism? Do they live in heaven as babies? If not, how would anyone recognize them?)
Evil then exists because god does not. Or, as Epicurus stated, any "god" that does exist is not worthy of being called "god".
Do you "believe"? How would you define heaven? How do you explain evil in the world?