Man cannot be free to love and serve God, without being free to reject Him and rebel against Him. We cannot have it both ways. Even God, if He wants men to be free, cannot take from them the power to choose evil.
If He enforces goodness, He takes away freedom. If He leaves freedom, He must permit evil, even though He forbids it. It is man's dignity that he is master of his own destiny instead of having to develop just like a tree which necessarily obeys natural law.
Men, as a matter of fact, misused their freedom, and sin and brutality resulted. But it was impossible to give man the gift of freedom and the dignity of being master of his own destiny without risking the permission of such failures