Because… they sure do seem to lie a lot.
You’d think for such an enlightened group of people, they would take lying a little more seriously. 
Examples?
“These aren’t the droids you’re looking for.”
“Darth Vader killed your father.”
“If you go to rescue your friends, everything you have worked for will be lost.”
“Into you Leia is; a shot you should take.”
I may be mis-remembering that last one.
Though Yoda never mentions this particular philosophy on screen, it’s clearly part of the Jedi code: The ends justify the means.
I suspected the first two would come up, but I don’t think they’re good examples of lying.
The first is suggestion. As soon as Obi-Wan says “These aren’t the droids you’re looking for” it becomes true.
The second can be excused as some vaguely poetic language.
I’d have to watch again to come up with excuses for the third.
I think the third one was a genuinely-held incorrect belief. Yoda thought that Luke going after his friends would end in disaster. He was wrong. When 900 years old you reach, screw up occasionally you will.
:dubious:
How does it become true as soon as he says it?
“… the droids you are looking for” applies to which droids, then?
“Darth Vader killed your father” wasn’t a lie if you look at it from the right point of view
when Anakin turned to the Dark Side, the good person he used to be died
From the right point of view, the “dog” really did “eat” your homework.
Jedis, like cops and soldiers, are there to save lives and solve problems. If a lie expedites this, so be it.
Come to think of it, “we did not come here to free slaves” was a pretty harsh truth…
If anyone’s curious, the Jedi code is (from Wookiepedia):
[QUOTE=Luke Skywalker]
Jedi are the guardians of peace in the galaxy.
Jedi use their powers to defend and to protect.
Jedi respect all life, in any form.
Jedi serve others rather than ruling over them, for the good of the galaxy.
Jedi seek to improve themselves through knowledge and training.
[/QUOTE]
Nothing about lying in there.
Just because Obi-Wan is capable of mind-controlling them into thinking the droids are a begonia and a Waldorf salad doesn’t change the fact that these are the droids they’re looking for.
Who knows? Not these droids. I dunno. Who cares?
I imagine the Jedi follow the same rules as most other people, where lying to enemies you would kill if necessary to achieve your goals is the lesser evil.
But the guards did not know those were the specific droids they were looking for. They only knew they were looking for a pair of droids of a particular description.
And how do you know Obi-Wan didn’t make them think they were a bowl of petunias and a sperm whale? 
Both Anakin and Obi-Wan lied about having girlfriends.
I wish I could come up with more specific examples. I just recently finished watching Clone Wars (Animated). I remember, I kept saying to myself: “There they go lying again.”
You misunderstand. I wasn’t questioning the ethics at all. There is a long-standing tradition of excepting life-and-death scenarios. Rahab the prostitute was considered justified by saving lives with a plain lie. I certainly would have applauded anyone who saves folks from the Nazis with a plain lie, or any other deception or evasion.
This was specifically address to what the logic was supposed to be: <<As soon as Obi-Wan says it, it becomes true.>> {paraphrased from the original}
And, BTW, (to others on this thread) the response from the guard shows that the guards saw droids, not a Waldorf salad, or anything else. (Yes, I know this and other items are meant as light-hearted examples.)
Hey that makes sense. It’s like when a president tells a whole country that another country has weapons of mass destruction and it’s our job to go in there and get 'em.
Wait a minute…
Deception in general is one of the Jedi mind-tricks. Obi-Wan howls like a [rancor?] to frighten off the Tuscan raiders. When Obi-Wan goes to disarm the Death Star’s tractor beam, he creates a audio illusion that makes the guards look the other way. Deception includes mind control: “These aren’t the droids you’re looking for” and whatever Luke says to Bib Fortuna (I don’t remember the exact words.) Lying is just one more form of deception. And it’s a tool in the Jedi arsenal, plain and simple.
Yoda is just plain wrong, on several counts. “I cannot teach him,” “He’s too old, too old to start the training,” etc. The explanation there is not that he’s lying to Luke, but that “always in motion is the future.”
Interestingly, the dark side Jedis seem to be more honest – what they say may be twisty, but it’s true (at least in IV, V, and VI – I only saw I, II, and III once each, and that was too many times)
I suppose you can explain the droid mind trick in two different ways. One is that the “victims” of the trick were consistent in what they were looking for, but Obi-Wan convinced them the gay robots in front of them were, in fact Cylons. The other is that the victims’ ideas about what they were looking for were altered. They could see the droids, but now they’re looking for toasters. I assumed the latter, probably without good reason.
I think C K Dexter Haven makes a great point about how the Jedi clearly embrace deception as one of their tools.
How about what Luke tells Jabba? “As a token of my goodwill, I present to you a gift: these two droids. Both are hardworking and will serve you well.”
(Hey, you know who served Luke well? Threepio. “Threepio, tell them if they don’t do as you wish, you’ll – become angry, and use your magic!”)