Very well said Gandalf
I can imagine my defense in a court if I thought like that .

Yes your honour the man I beat to death with a baseball bat was looking at me like he wanted to kill me.
Judge : He was serving you coffee.
Yes your honour but I felt threatened because I thought he might have a weapon.
Judge :You were in a coffeeshop.
Yes your honour but I was certain in my mind that he was going to attack me so I went home , got a baseball bat and smashed his head in just in case he did want to attack me.

I can't see the judge saying "okay man just go home , he deserved his skull bashing in for looking at you like he wanted to kill you ".