Nineveh was an enemy of Israel and the peoples wickedness in Nineveh came up before God and God told Jonah to go there and warn them of their fall. But he didnt do it because he was afraid that the enemy nation should repent and receive Gods forgiveness. In mans view what Jonah did might look acceptable. But, any disobedience to God in itself is evil and by extension it is goodness to save as many people as possible by giving the opportunity to repent though they are against us. Hence we should always follow the Word of God without swaying in the wrong standard of good and evil.