Well he didn't leave that map to find him. It was a map to the first Jedi temple that Lor San Tekka had acquired. Han knew that's what he was looking for, so the assumption was Luke would be there.
I've had this debate a number of times, and impossible to really be correct or incorrect because it's based on your personal belief of what the impacts of that event would have been.
Yes, Luke was an optimist in the early days. But I don't see it as a simple failure. He thought he could build a new Jedi order based on his limited training. He took his nephew under his wing and managed to lose him to the dark side. I'm not sure if anyone in this conversation has kids. But imagine holding yourself directly responsible for the loss of your sisters only child. Imagine saying you'd protect them, deeming yourself wise and powerful enough to guide them, but then due to your own weakness you actually drive them away.
Guilt and shame are powerful motivators. Luke didn't just blame himself for Ben's turn, but also then saw himself as a risk to any other powerful force users who might seek him out. If he couldn't guide his own blood, how could he be trusted to guide anyone else.
I feel like people overlook that all his optimism in the OT was external. He was putting faith in others. Faith in his father, his freinds, his teachers. But not really in himself. He seemed to always have that bit of doubt. Whether it was his inability to find a new life on Tattoine. His difficulty in training with Yoda. And with his fear to confront Vader in Jedi. In Empire and Jedi one of his primary motivations is his fear that he is the cause of danger for others. It causes him to abandon his training and confront Vader too early. It causes him to turn himself in on Endor. He is constantly worried that he will somehow be the downfall of his freinds and family.
And in training Ben, that finally happens. No he wasn't responsible for his turn. But that momentary act of despair that caused him to take out his saber, caused a ripple effect that destroyed thousands if not millions of lives. That's a pretty big weight for someone whose main fear has always been inadvertently causing harm to others. And he thought he had the key to stopping that from ever happening again in locking himself away.
