To Help

If someone comes to kill is, we understand that we have the right, and even the responsibility, of self-defense (Berakhot 64b, Sanhedrin 74a).  When others are threatened, we are called to help them as well.  "Do not stand idly by your neighbor's pain." (Leviticus 19:17-19)

This is not an option.  It is a mitzvah.