[recondite7]

You are giving him the opportunity to bluff off his stack when a scare card hits on the river if you just flat call. If you read him as that aggro flat call and evaluate the river but i'm not nec going to fold to a push here when the third flush card comes.

On the other hand a good player could see your flat call as strength and check the river to you which basically accomplishes the same purpose of pushing him out of the hand on the turn.