Even in Diarra's most amazing game ever the other day, he was still unusable in the first half.
There are very specific situations where Diarra's skill set on defense is a perfect fit and it make sense to use him.
But bad Diarra is really really bad. He gets out of position, he acts all confused, he'll turn it over a ton.
If the opposing team ever throws it to the low post on offense, thats not likely to be a game Diarra plays a lot.