How can Finn refuse to kill?

The whole premise behind the Star Wars: The Force Awakens Stormtroopers is that they are literally mindless minions, who know just one thing: those who aren’t with the First Order are enemies which need to be destroyed. Raised by the Order from the moment they are born (or thereabout), the Stormtroopers are inoculated with the propaganda for as long as they live.

If so, how come Finn manages to overcome the brainwashing and even think about deserting? We see that the Stormtroopers who misbehave are called in and brainwashed again. Can Finn resist repeated procedures?

Furthermore, when the Stormtroopers are slaughtering civilians and after Finn refuses to shoot, Kylo Ren stops and glances at him, as if he recognized a Force sensitive person. What does it all mean?

We have no answer for this questions, outside of the movie itself. Finn will return in the sequels – will there be a satisfactory conclusion to his story? Will we find out how he managed to free himself? Most importantly, is he Force sensitive?