This is a basic question and a standard excuse for atheist to be atheist. They see themselves as more moral than God, because they would not allow the innocent to be hurt. However, they do not understand God, or why He allows sin and because they have decided not to honor God, they cannot understand.
As I have said before “God lives by His own rules”. I would use the word “laws”, but that word brings a knee jerk reaction among Christians that have not yet contemplated God’s law.
A long time ago, when I was young, someone (I do not remember who), told me that if I wanted to understand something that someone else said, or believed, or even did, that it would help, if I tried to think as they do. You have probably heard it said as “Walk a mile in their shoes”. I have found it to be very helpful, not only for understanding others, but also for understanding God.
Now, before you go off on a tangent and say that we cannot understand God, and what He does, I must point out that He has given us a manual and a teacher, so that we can understand. That is how I know that He lives by His own rules and when you contemplate His Word and listen to the Spirit that lives within you, then you will also understand. Not because I said anything, but because you searched it out yourself: with the help of the Spirit.
God’s rule for dealing with others is “Do to others as you would have them do to you” It is a plain and simple rule that fits all interaction among people. If anyone follows the rule, or obeys it, then it should be obvious that we do not need the Ten Commandments. All of the law hangs on this Command. If we obey the second most important rule, then there would be no murder, thefts, or any other sin.
OK, so you ask ‘How does this relate to why God allows sin’?
Do you want anyone to force you to do anything? Of course not, so keeping the second greatest command in mind, then you should not force anyone to do anything.
God does not want anyone to sin, but He lives by His own rules and His rule prevents Him from stopping anyone from sinning.
Those who do not know God only see the physical world and do not understand that God made us to exist forever, so if someone is mistreated in this world, it seems to them as a terrible thing: and it is. However, we will go on to the life after this part and we will understand that all sin is really against God, more than against the person.
If someone should steal everything that you have, did they really steal anything from you? If God owns everything, and He does, then what can anyone steal from you?
The same goes for your life! Did you give yourself life, or did God give it to you? Anyone that steals, or murders, sins against what God has created. That is not to say that we do not suffer because of sin, but it helps to know that God will dry our tears and make us forget the sin of this world.
Do not look for your reward in this life. Have faith in your Father. Hebrews 11:39&40 (NIV) “These were all commended for their faith, yet none of them received what had been promised. God had planned something better for us so that only together with us would they be made perfect.”
Everyone, that God saves, will live by His law and there will be perfect peace in Heaven.