Sorry... I may have misspoke... err... typed... You're right in that Luke did not attempt to kill his nephew, in that he never engaged in the act of killing Ben... it's of course small comfort to Ben who woke to see his uncle standing above him visible by only the green glow of the lightsaber that Ben thought was about to end his life. On a related note, I wonder what exactly Luke had told Han and Leia about that night? In the TFA, both Han and Leia knew that Ben had turned, however neither of them seemed to hold Luke responsible (Han stated that Ben had too much Vader in him and Leia said it was Snoke). That means that either both are of an extremely forgiving nature or Luke never told Han and Leia the whole story.