Self-defence

At some point it comes to this. It’s akin to an implementation of martial law. A terrorist or a freedom fighter, a good guy or a bad guy – none of it means anything.
All the context I need to make a decision is:

He’s armed and threatening to kill people.
He’s desperate.
He’s a danger to me.

I’m not a terrorist or a freedom fighter. I’m not an arm of law. What I am, however, is a rational being, and in my mind that authorises me to become judge, jury and executioner before I am the one judged and executed.