Everybody makes mistakes. The Bible tells us that, "For everyone has sinned; we all fall short of God's glorious standard" (Romans 3:23). God created everyone on the earth, and He loves every single person who has ever been born. He knew that the people of Nineveh had sinned. But He also knew that the people of Israel had sinned. His mercy for the people of Nineveh was as great as His mercy for the people of Israel -- that is why He sent Jonah to warn them. He wants everyone who does wrong to repent and say they are sorry, so that He can continue to bless them.
The wonderful promise from the book of Psalms tells us, "For his unfailing love toward those who fear him is as great as the height of the heavens above the earth. He has removed our sins as far from us as the east is from the west" (Psalm 103:11-12). So if you see someone doing wrong, don't judge or criticize them. Pray that they would do right and say they are sorry for their sin, just like the people of Nineveh did.