We don't know who invented the doctrine of infant baptism in America, but we do know who promoted it in Europe. It was Bishop Augustine around 300 A.D.He became extremely influential with the church in Rome and eventually used the sword and the threat of the inquisition, which meant torture or burning at the stake, in order to force European Christians to accept infant baptism. Augustine taught that Adam's transgression in the Garden of Eden left a curse on all mankind and unless children were baptized in their infancy they would be consigned to purgatory forever.
Somehow, Satan planted the same false and wicked doctrine among the Christian Nephites in America. It seems to have gained a foothold shortly after Moroni was called on a mission. Mormon therefore wrote to Moroni so he could explain to the Saints why this doctrine was a satanical error.