"One who plans to do evil, men will call a schemer"
The word plan is the word for thinking, imagine, and devise. It does mean plan, but it can also mean daydream and fantasize. The person who is always fantasizing about evil will end up committing some form of evil. At first the only evil they commit is not accomplishing the good that they could have been doing. But eventually the lure of actually doing evil draws them outside of the boundary lines of God.
We must not allow our present culture to define what is evil. For their boundaries are much further out than God's. We will never understand why many of the negative consequences flow around people until we understand where the real lines of good and evil are. In the Old Testament, Moses and the prophets consistently said that good was positive action within the Ten Commandments and evil was any action outside of those boundaries.
In our day and age, we do not want to acknowledge adultery as a moral boundary. We don't want to acknowledge swearing, cursing, and oaths as immoral behavior. We do not want to understand that idolatry and sorcery are evil endeavors and not harmless parlor tricks. We do not want to admit that covetousness eats away at a real life and is evil. Instead we celebrate the advertisers who can get us to covet almost anything. Living outside of the boundaries of the Ten Commandments is like living in an unwashed jungle. The jungle will destroy you.
The sad thing is that some people spend a lot of their time thinking about how to get out to the jungle and how to shed the "restrictive" rules of their parents and puritanical society. But then once they are out there, then the consequences of jungle life begin to set in. Also, if you are out there, there are slave labor camps seeking to capture the unsuspecting. We call these addictions.
men will call him a schemer
The translation of this phrase does not do justice to the impact of what is being taught. The word schemer is really the word baal or the word for the god of the underworld and perverse sexuality. The proverb is really saying that if you spend your time planning and thinking about how to live outside of God's box, people will call you the Devil. You will be doing his bidding in this world. You have become his agent in this world.
In other words, you are in league with the Devil if you give yourself to planning actions outside of the Ten Commandments. This means that if you spend time planning how you would like to kill your boss (even though you wouldn't do it), you qualify as the Devil’s agent. If you spend time planning the seduction of a married man or woman (even though you would not do it), you are in the Devil's employ. If you spend time planning how you are going to rebel from parents, government, or employer, then you are joining forces with the wrong side.
The god Baal in the Old Testament was the Sun God and yet the God of the underworld or after-life. He was offered sacrifices of newborn babies seared alive on the arms of this fiery idol. He was also referred to as the god Molech. (Jeremiah 19:5)
Spend time planning righteousness. Don't get lulled into thinking that you can think anything you want as long as you would never do it. That is just not true. Instead, plan and think and fantasize about good things and right things that are within the boundaries of the Ten Commandments.