I don't know why Kakashi doesn't simply get Deidara out of the sky with a kunai. After all, with his Sharingan he should be able to read Deidara's movements to a sufficient degree to compensate for evasive actions.

But I guess when Naruto has pleaded him to return Gaara for the 2000th time, even Deidara will get pissed off enough and come down voluntarily to shut Naruto's mouth. I know I would. And much sooner.