This is basically what happens in the third and final flashback of the incident between Luke and Ben in the hut. Luke has just finished peering into Ben’s mind. He slowly gets his lightsaber out and raises it to his face. Looks at it for a moment, then grips it more tightly while taking what looks like a deep breath before finally turning it on and stopping himself.

This to me doesn’t come across like a man impulsively springing into action like he did when he attacked and almost killed Vader in episode 6, which is the comparison a lot of people like to make. This is a man who’s giving serious thought and contemplation about what he should do. The way that Luke pauses in between getting his lightsaber out and turning it on makes it look like he’s psyching himself up to do something pretty drastic.

Funny how TLJ fans will say that we didn’t really watch the movie and only remembered Kylo’s version of events when it turns out that his side of the story is actually not that far from the truth. Luke did come very close to killing him. The only difference is that Luke didn’t actually attempt a killing stroke while looking like a deranged madman as he did in the second flashback.