Many Christians are of the opinion that God has written His laws on the hearts of every man so that they may know right from wrong. The classic proof text is from Romans where Paul is discussing the extent of the sin in the world. I am not convinced that this passage teaches such an expansive idea.
Earlier in Romans, Paul describes how everyone knows from the creation that there is a Creator, but they suppress that truth in unrighteousness—knowing that if there is a God, they are accountable to Him for their actions. God has made it plain to them that He is the Creator and that He is powerful (Romans 1:18–32). Everyone knows there is a God who created this world—they either acknowledge Him in some form or suppress that truth because of its effect on their life. There are no atheists!
But, does this mean that everyone knows right from wrong?