The line “once you start down the dark path, forever will it dominate your destiny” is also misinterpreted. Yoda isn’t saying literally any time you get angry or use the Force in anger, you’re beyond hope or redemption. … The consequences of your actions will still be there.
I don’t agree. The full line is “Once you start down the dark path, forever will it dominate your destiny. Consume you, it will! As it did Obi-Wan’s apprentice.”
Specifically look at Yoda’s usage of the word “consume”. Your actions and your decision making will eventually be completely affected by the dark side. It isn’t just that your life is marred by the consequences of your actions, although it is that too, he’s saying that you can’t just dip your toes in the dark side. It’s something that’ll pull you further and further in.
After Return of the Jedi, there’s irony in referring to Darth Vader because he does return to the light. But Darth Vader is, at this point in the story, fully committed to evil. Yoda brings him up to emphasize that once you turn to the dark side, you inevitably become like Darth Vader.
I’ve ranted about this many times before, but Yoda and Obi Wan were not telling Luke to kill Vader.
Luke: “I can’t kill my own father.”
Obi-Wan: “Then the Emperor has already won.”