I think that's a bit harsh. Wragg didn't 'look ignorant' at all! We all know that backbench MPs do not generally ask questions of the Prime Minister in order to receive new information, and indeed Cameron did not say anything in his reply which Wragg and the rest of us didn't already know.
When backbench MPs pop up at PM's Questions, their purpose is simply to demonstrate to their electorate that they are busy representing our interests. In other words, it's purely for show. That's not a criticism, it's just how things are.
Wragg was elected with a clear majority, and we should give him a chance to show what he can do, even those of us who didn't vote for him!