Honestly, when you consider the damage the Jedi have wrought in the name of the light side, scrapping the Jedi Order might be the best option. "It's time for the Jedi to end" could be Luke's way of saying that the only real hope for peace in the galaxy is complete abstention from Force manipulation. Rid the universe of Jedi, torch the Jedi Academies, bring down the Sith copycats, and there's no one left to turn (or be turned) to the Dark Side. It's a logical conclusion for a Jedi Master in his place to draw.
Here's a guy who fought the Empire, led many Rebel soldiers to their deaths, defied his own father in the name of the light side of the Force, and for what? Thirty years later, things are worse than ever, with the First Order picking up where the Empire left off. When does it end? Why even go on teaching this stuff, when someone always turns to the dark side and starts a war? "This pupil could very well become the next threat to all life in the galaxy, but whatevs! Three cheers for kyber crystals, robes, and trusting in your feelings!" Sure, lightsabers and telekinesis are awesome, but is it really worth it the next time a Sith lord is taking over the galaxy?