If God is Good, why does He allow evil? (Q raised in a debate.)

If God is Good, why does He allow evil? (Q raised in a debate.)
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The answer is that a good God may allow evil if He has a good reason. And we need not know God's reasons for allowing evil, because Allah says in the Quran that we are given only very little knowledge:

*{…of knowledge it is only a little that is communicated to you, (O men!)}* (Al-Israa' 17:85)

Therefore, it would be enough if we know of a possible reason for God to allow evil to exist. And from the Quran we can understand that Allah has given humans free will, in order to test them to prove who is better in good deeds:


*{Every soul shall have a taste of death: and We test you by evil and by good by way of trial; to Us must ye return.}* (Al-Anbiyaa' 21:35)
One consequence of freedom is that humans may choose evil instead of good. But if they are forcefully prevented from choosing evil, there will not be any freedom. That is to say, God cannot have free beings whom He forces to choose only good; because, that would involve a logical impossibility.
As intelligent beings we know that most of the things that make life worth living require that we have free will. Moral responsibility, sense of individual achievement, satisfactory personal relationship, and so on, are a few valuable things that cannot be without freedom of choice.
We know fire is useful because it burns and helps us cook our food; but the same burning quality of fire can burn down homes. That is to say the very things that are useful for us can inevitably cause damage too. Now can we completely dispense with fire as it has a destructive side?
For instance, to rescue a drowning man is good work; but this is possible only when someone is drowning, which is a bad thing. That is to say, we have a chance to do good work only when there is a need, which in itself is "evil", or at any rate not "good".
An example of natural evil is a flood in which many people including children suffer. A believer in this context does not curse God; because he takes it as a test of his faith. Instead, he goes out to help the victims in whatever way he can. And thus he draws near to Allah and is successful in that test.
In short, without evil, there is no good. And both are equally necessary for the spiritual development of man. For the spirit to grow, it has to overcome evil and do good.

“Nay, seek (Allah's) help with patient perseverance and prayer: It is indeed hard, except to those who bring a lowly spirit….}* (Quran, 2:45)

“On no soul does Allah Place a burden greater than it can bear.” (Quran 2:286)
Hope this guides better to the question, thanks.