I don't think evil is man-made.

but I think humanity is a force for good, God's children.

This is a nice sentiment, but it is incongruent with reality and with Scripture.

They are all gone aside, they are all together become filthy: There is none that doeth good, no, not one. Psalm 14:3

They are all gone out of the way, they are together become unprofitable; There is none that doeth good, no, not one. Romans 3:12

The fool hath said in his heart, There is no God. Corrupt are they, and have done abominable iniquity: There is none that doeth good. Psalm 53:1

He was in the world, and the world was made by him, and the world knew him not. He came unto his own, and his own received him not. But as many as received him, to them gave he power to become the sons of God, even to them that believe on his name: which were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God. John 1:10-13

The Bible teaches that all men are evil and destined for death (both physical and spiritual). Only those who are born again are called the sons of God.

While Satan and his minions can influence men, we do not know the limits of this influence. Plenty of people in scripture commit truly heinous acts, and rarely (if ever) is Satan blamed for it. Mankind, through our own free choice, is capable of plenty of wickedness without Satan's help.