Such an argument may at first seem very compelling, particularly when you are suffering from a bad toothache. However, there are two thought experiments one can try that seem to greatly weaken such an argument. After we try either thought experiment, the argument from evil seems much less compelling.
Thought Experiment 1: The Question at the End of the Billion Years
To do this thought experiment, you must imagine that it is a billion years in the future. Imagine that you died after living out your mortal life, a life including great hardships and suffering. Imagine that you then found yourself in some kind of blissful afterlife. Imagine that your mortal life of hardships was followed by a billion years of glorious, wonderful happiness in some heavenly afterlife. Imagine also that your relatively brief earthly sufferings gave you a greater appreciation of your happiness in this afterlife, simply because someone who has known suffering is more likely to appreciate and enjoy happiness than someone who has never known any suffering (the latter person being more likely to be jaded and unexcited about any happiness he experiences).
Now the question to ask yourself is: at the end of this billion years, would you look back at the first 70 or 80 of these billion years and say to yourself: the fact that I suffered then suggests that there is no God?
The answer to this question is: no, you would not. Indeed, after the end of such a billion years, such a question would seem almost absurd.
Now a critic might suggest that it is not fair to ask this question, on the grounds that we have no evidence that people will experience such an afterlife. This is actually a most debatable assertion, as there does exist what many argue is a significant body of evidence (including near-death experiences) that may well suggest a strong possibility of an afterlife.
Also, the possibility being mentioned here (that individuals will experience a long blissful afterlife) cannot be excluded by anyone arguing against the existence of an all-powerful loving God, given that such a possibility may well be a consequence of such a being's existence, or something that tends to follow from the existence of such a being. If X tends to follow from Y, and you are arguing against the existence of Y, you cannot exclude the possibility of X while you are debating whether Y exists. All consequences (or possible consequences) of a particular hypothesis must be “on the table” whenever we are considering whether that hypothesis is correct. So the possibility that everyone will experience a long blissful afterlife cannot be excluded as a non-possibility while we are debating whether a particular argument against the existence of God is valid. In short, it seems quite legitimate to evoke Thought Experiment 1 in the context of this discussion about whether the argument from evil is a good argument.
Thought Experiment 2: A Human Race Enjoying Perpetual Orgasmic Pleasure
Those who say that evil and suffering argues against the existence of God often speak as if maximizing pleasure and minimizing pain would be the chief ends that any good and omnipotent deity would pursue. So let's go forward all the way with such thinking. Let us imagine an Earth on which every person experiences the utmost pleasure every day, along with absolutely no pain. We can imagine exactly how this might work.
Let us imagine a planet Earth on which every human spends his or her entire life lying in bed. Each person is connected to a brain stimulation machine which sends out an electrical current that stimulates pleasure centers of the brain. It is, then, as if you are experiencing an orgasm all day long. But it is even better. Imagine that the brain stimulation machine produces the utmost pleasure for every person who uses it, better than the pleasure someone can get from heroin, cocaine, or the best sex imaginable.
Let us also imagine that the people lying in bed never get tired of this stimulation, that it is always as thrilling and pleasurable as it might be the first time. Let us also imagine that people don't mind lying in their beds all of their lives, and that they don't need any exercise. We can also imagine that the Earth is populated by robots who take care of all human needs, keep the electricity running, and give us humans daily injections which give us the required nutrients and water.
Under such circumstances, every human would experience the utmost pleasure all of their lives, and no human would experience any pain. So, this ultra-blissful ever-orgasmic existence would be something like an ideal existence for the human race, right?
Wrong. I'm sure most readers will be disgusted by this concept of human existence. The average person will have a very strong kind of intuition: no, no, no, that is not how the human race should ever exist.
But let us analyze: why exactly is it that we sense so strongly that this “perpetual orgasm” existence would not be a good existence for humans? If we figure this out, it may actually shed insights relevant to the problem of evil.
One reason why this “perpetual orgasm” existence would not be a good existence for the human race may be that diversity of experience is very important. One problem with the perpetual orgasm scenario is that if it existed we would live lives that are pitifully limited in terms of diversity of experiences. Even though we can't say exactly why, we can somehow sense that it is somehow better to live lives that are rich in many types of experiences.
Another reason why this “perpetual orgasm” existence would not be a good existence for the human race may be that we put a strong value on overcoming difficulties. The people we admire the most are those who have overcome great difficulties, moral, social, or physical, not people who have always lived in the lap of luxury without any setbacks or hardships.
Another reason why this “perpetual orgasm” existence would not be a good existence for the human race may be that we think the most meaningful moments of our lives are those that involve helping other people in need, but there would be no opportunities for such moments if everyone spent all their lives living in perfect bliss.
Still another reason why this “perpetual orgasm” existence might not be a good existence for the human race may be that mankind's proper purpose (in the long run) is not to merely “bliss out” but to play a role in some stirring cosmic drama, some epic tale of evolution and progress, a far-flung galactic saga in which evils are gradually defeated and hard-won triumphs and glories are earned after a struggle involving great difficulties.
In light of such insights, perhaps we should abandon the simplistic assumption that if there existed a God that deity would give us lives of perfect pleasure and no pain. Perhaps instead such a deity might create a universe that did offer a rich spectrum of experiences, that did offer many chances for overcoming great hardships, that did offer abundant opportunities for helping others in need, that did include opportunities for rising from lowly or sad states to higher and happier states, that did include the possibility of species such as ours participating as heroes in some glorious epic of progress and galactic evolution.
Such a universe might even be...our universe.
Ad astra per aspera