Minor spoiler, obviously:
At the beginning of the movie, Finn doesn't shoot during a massacre. My first thought was this was a mistake on the part of the writers—it would be more discreet if he shot over the heads of the targets. But then I realized that would mean Finn was being cunning rather than viscerally unable to slaughter defenseless people.
And then I remembered that in actual combat, a percentage of soldiers never shoot and others shoot to miss. They may be the majority. The exact numbers are fiercely debated; if you're curious, you could start researching here:
True or false: "Soldiers tend to intentionally fire over the enemy's head, or not to fire at all." - Straight Dope Message Board
Economist's View: Manufactured Contempt and Its Consequences
In any case, all those storm troopers who shoot and never hit the movies' heroes? They may just be good people who believe all lives matter.