What is the rationale behind disallowing forward laterals?

Answer 1

There's no such thing as a "forward lateral"--that's a contradiction in terms. If you throw the ball to another player who is closer to the opposing end zone than you are--even if he's only closer by one step--that's a forward pass. If you throw the ball to another player who isn't closer to the opposing end zone than you are--a player who is even with you or behind you--that's a lateral.

If there was no prohibition against 'forward laterals' then the game would become simply a game of 'keep away', with players routinely tossing the ball to any available teammate anywhere on the field. Then what do you do with the 'pass interference' rule? If a player gets blocked just before he's tossed the ball, would we award him 15 yards and a first down?

Allowing a 'forward lateral' would fundamentally change the nature of the game.