Yeah, I've laughed at the explanations given in the past about why Yoda and Obi-Wan (and the entire Jedi Order for that matter) don't simply kill Vader before or after he helps murder all the Jedi. I mean, if Yoda and Obi-Wan are supposed to be two of the greatest Jedi in the history of the Order, I would think the two of them should be able to handle 1 Sith in the 18 years between films. Or for that matter, train Luke when he is younger as opposed to waiting until he is 18, much older than the 'too old' Anakin. Sounds like they had a real good plan working there.

This has been explained in the past as 'not in their nature'. Of course, it hasn't stopped Obi-Wan from chopping Maul in half (out of anger **very un-Jedi**).

Another explanation is Obi-Wan's line 'there are alternatives to fighting'. Yeah, like what? Allowing the Galaxy to be controlled by the iron fist of Vader and the Emperor for 18 years while you wait for 'the chosen ones' guardians to get charred by Galactic Stormtroopers?