People should be able to see beyond doors that open to the outside. Windows in or beside (called sidelights) the door is a simple security feature. The ability to see what’s on the other side of a door without opening it to potential unknown visitors is smart.
Peep holes are a great idea for multi-family buildings or areas that need more security, but keep in mind that they need to be usable for everyone. A peep hole may be difficult to use for individuals with low vision or those who are unable to use it if mounted too high. The easiest solution is to just drill another hole and install a second at a lower height.