Good people are needed in this world for various reasons. One reason is because they make the world a better place for everyone around them. Another reason is because they put a stop to bad people wanting to harm others.
If they were more good people in the world there would be less violence & negativity around the world. They radiate positive energy instead of negative vibes. Which causes other people around them to do the same. Just like they say a smile is contagious so are positive people. Good people just want to help others and stop bad people from causing harm. An example of this is police officers, doctors, teachers,etc.
As for bad people that spread fear and violence to everyone near them which nobody wants. They don't like to see others happy. They want to see people hurting for their own benefit. Therefore it causes people to be concerned for their safety and nobody want to live their lives in fear and worrying about their lives.
Although not everyone is technically "good" their are such things as good intentions and actions. Which inspire others to do others the same just like John Quincy Adams said "if your actions inspire others to dream more, learn more, do more and become more you are a leader". This quote shows how being a "good person" does do justice and good for the world.
Good people do good things and they change the world by their admirable actions. One small action can trigger the world to change for the better. So remember that next time by doing a nice gesture you can change in the environment and start a chain reaction.