[Bartholow]

It seems to me that a) someone will bet this turn and b) it doesn't seem likely that your bet would get a diamond to fold that won't fold if someone else bets. Therefore checking and calling has the advantage that you can't be raised, and if it goes bet-raise you can fold, since the raiser is supposedly loose passive.

If there is a chance of a free card, I think you should bet. If you think someone will fold a hand with significant outs because YOU, the preflop capper etc., have continued firing, then I think you should bet. But it doesn't really look like that's the case here.