If the public moves away, then the quantity of transactions will drop.  If there are less transactions, then it won't cost as much (in transaction fees) to get your transaction confirmed.  If it doesn't cost as much, then the public will choose to use Bitcoin.  If the public chooses to use bitcoin, then the nuber of transactions will increase.  If the number of transactions increases, then it will cost more (in transaction fees) to get your transaction confirmed.  If it costs more to get your transaction confirmed, then the public will move away.