Without that, what else is there?
There is sin. "Original sin" and "sin" aren't identical. Adam doesn't need to have to have sinned in order for another individual to be guilty of sin. http://en.wikipedia.org/wiki/Semipelagianism
The beliefs of the christian community are far from homogeneous.
Also the "original sin" mentioned in the GGP seemed to be the Calvinist version of it which is quite different from the Arminian version of original sin, to the point where many Calvinists will claim that Arminians don't believe in original sin.
There is no royal road to geometry. -- Euclid