Software should be free.This free does not mean that it is priceless but that it should be accessable by as many people as possible.

A very good example that can explain this is about the road.If the road is charged,its construction will be more expensive because fewer people use it while the total cost remains the same.

As well,three levels of material harm will come from the obstruction:
1.Fewer people use the program.
2.None of the users can adapt or fix the program.
3.Other developers cannot learn from the program,or base new work on it.