This question has always been predicated on a false premise, that is, that God is the ruler of the earth. He is not, the devil is in charge. So if God is all-powerful, why doesn't He do anything to stop the evil? That is also an assumption that God has no choice in the matter. He chooses to back off and let the world go its way via its free will to choose, and take unto Himself those that choose Him despite the evil around them. It's not like this is the end of the story, there remains a day when God will cast all evil into a dimensional plane that is called "outer darkness".
Jesus told a parable regarding the sowing of tares (fruitless weeds) amongst wheat. When they first germinate, tares look just like wheat, so it is incredibly difficult to weed them out. Fortunately, once tares mature (near harvest) they turn black. In the last days, there will be a chasm between those with fruit and those that do not. One group will be harvested and winnowed, the other will be cast into the fire for consumption.
Consider, however, that the wheat still requires winnowing to remove chaff from the grain. That too is happening. http://www.schneblin.com/studies/pdfs/winnowing_wheat_chaff.pdf
Evil is necessary for free choice to be a reality. You can choose which side you wish to be on. And in reality, that is what you are seeing today. People choosing their sides. Again I will say that this world does not belong to God. Satan is the god of this world. So, give credit where credit is due.
Luke 4:5
Then the devil, taking Him up on a high mountain, showed Him all the kingdoms of the world in a moment of time. And the devil said to Him, “All this authority I will give You, and their glory; for this has been delivered to me, and I give it to whomever I wish. Therefore, if You will worship before me, all will be Yours.”
1 John 5:19
We know that we are of God, and the whole world lies under the sway of the wicked one.
But one day soon, that will all change when Satan is cast out as the usurper he is...
Revelation 11:15
There were loud voices in heaven, saying, “The kingdoms of this world have become the kingdoms of our Lord and of His Christ, and He shall reign forever and ever!”
...and then the healing will begin.
Revelation 22:2
The leaves of the tree [of life] were for the healing of the nations.
