I think it is fair to say this is one of the most difficult problems for Christians to deal with.
Some philosophies are still trying to figure out what is good and what is evil, others such as Scientology deny the existence of reality. But Christianity must come to terms with the fact that they have defined good and evil, they believe it actually exists and they believe in an all good all powerful God who seems to be standing by watching with His arms crossed while bad things happen to the innocent.
Asaph complains of the same thing in
Psalm 73. He wants to know why the wicked prosper and the righteous suffer. We as humans want to scream at God, "That's not fair." If this life were all that there was we certainly would be justified in our accusation. But like Asaph observed "Then I saw their end."
Without the vantage point of eternity it is arrogant to complain to God, "that's not fair." We believe that an all loving, all powerful God will one day destroy evil and wrongs will be made right. So it is not that God is either not loving or not powerful enough to destroy evil it is that he has not YET destroyed evil.