All right, guess I'll wade in to this.

First of all, there's a difference between agreeing with what Luke did and understanding what Luke did.

Luke tried to restart the Jedi Order after defeating the Sith and the Empire, ending a conflict that spanned millennia. He did this with knowledge of why the older Jedi Order fell and how their failings led to Sith domination of the galaxy.

In his very first batch of students, literally his own nephew falls to the Dark side and kills all/most of his other students.

Luke is jaded because he thought he had solved the problems that led to the destruction of the Jedi and rise of the Sith. Instead, he gives rise to a Sith and re-destroys the Jedi.

The only other Jedi that Luke has ever known were in hiding and had basically given up fighting the Empire, because they had failed in their mission as Jedi. Is it really any wonder that Luke decides to the same?