Enjolras values conviction, beliefs, courage; he values pragmatism also. Those whose spirits are willing and their abilities weak are to be pitied and respected in equal measure; those whose hearts waver but whose actions serve good ends may find their courage strengthened in time by others' examples, and the good they've done will remain.

Grantaire, so far as he has ever seen, has little enough of either conviction nor action.

His question, then, is exasperated, but it's genuine:

"Can you be good for something?"

Or, more to the point, will he?