Keeping a Player Honest

There is a certain logical absurdity about the trying to keep a poker player honest. The sport of poker has lying to your opponents built right into the culture of the game, so trying to keep someone honest is at best a futile act. So why do so many players waste money at the end of a hand trying to do just that? Let's say you are at the river and in a position where you are trying to decide whether or not to call someone's bet or raise. There is a percentage of players out there who know they are beat at that point, but will still make the call in order to force their opponent to show their hand.