pablumatic said:

For being one with the Force Obi-Wan seemed more out of tune with it than Luke in Return of the Jedi.

Obi-Wan wants Luke to kill Vader. Luke doesn't want to and eventually doesn't have to. Being a spirit residing within the Force Obi-Wan appears unable to foresee any other alternatives to their fight than Luke using lethal force. Whatever happened to trusting your feelings or wars not making one great?

Obi-Wan's line after Luke tells him he can't kill his father: "Then the Empire has already won." should have been left out and something else put in like "The alternatives to fighting Vader won't be easy but I'm not against you seeking them out."

The point is that it was established that once you fall to the dark side there is no way back. Obi-Wan was just being realistic about it. Realistically, in this case an alternative to fighting was letting the Emperor win. Anakin being able to come back to the light side should be seen as an unique accomplishment.

The EU of course completely degraded this concept.