Okay, I gotta give credit where credit is due. This is one of the best defenses I have seen for this particular issue.
However I feel it can't be a fair comparison because Luke was still young and had a lot to learn. Yes he nearly fell to the dark side when dueling Vader but he overcame that moment. And while getting fried by Palpatine he didn't even try to fight back.
Vader had done a host of evil things. But Kylo hadn't done anything yet. He just showed an inclination of turning to the dark side. Luke was in a life and death duel with Vader. And Vader taunted Luke by threatening to turn his sister to the dark side. Which I think spurred Luke into more aggressive fighting. Kylo however was just sleeping. And Luke being a much older and wiser Jedi should not have responded that way to Kylo. Why didn't Luke try to kill Palpatine after defeating Vader? He didn't want to kill Palpatine because to attempt doing so would have meant Luke giving into the dark side. And he was a Jedi.
Luke being an older and wiser Jedi should not have been tempted, let alone giving into that temptation, to kill a boy showing an inclination of turning to the dark side.