Except every other victim we've ever seen possessed by the Sha became basically a living version of the emotion that was made manifest. They acted illogically and blindly, disregarding all other emotions and senses. Being able to lie while under Sha possession implies that the victim still has control over their thoughts while possessed, which has been shown many times this expansion that they don't.
You're disregarding everything we've seen and read in Pandaria regarding the Sha.