Originally posted by steverules_2
You must have missed the post where I said that Luke beat Vader with anger when Vader mentioned turning Leia to the dark side. And Luke did reject the dark side in ESB, vader tried to turn him so that they could both take down the emperor and rule the galaxy as father and son. He decided to jump rather than turn to the dark side. Yeah, he nearly turned to dark side but the fact still remains that he didn't turn.
Yeah, but that doesn't mean Yoda & Obi Wan weren't rightfully worried in TESB that it could go wrong for Luke in the crucial moment. The potential was there. You can't just say "Why were they so worried about Luke turning to the dark side? I saw Return Of The Jedi, and he didn't turn."
One major difference between Anakin & Luke, is that Anakin had killed people using the force in anger & in fear. His years of intensive Jedi training may have helped him get over the incident with the Sandpeople (plus, he was remorseful), but by the time he aided in the death of Mace Windu, he had gone too far and fallen to Palpatine's influence.
If Luke had kept going and killed Darth Vader in ROTJ rather than just sever one of his hands, he was throughly consumned by anger & fear in that moment that he could have fallen the same way. But Palpatine's goading made him pause, and he caught himself just in time.