Mutiple authors = mutiple beliefs. Simply because it is written by many people, does not make it that it is what Jesus wanted. Can you say its the 100% belief of jesus?
1 guy writing a religious scripture of his OWN RELIGION is more credible, than 40 writers writing a scripture for someone else's religion.
The authors were inspired by God and the Holy Spirit (someone already posted this). Their stories all coincide with each other. That's quite remarkable for being "different beliefs." They're different perspectives, yes, but they back each other up. So...
A single man's religion cannot be more credible when they claim to be inspired by God. It isn't, therefore, their religion, but God's. So...
Also, there is no person to hold the one writer accountable, seeing he wrote it himself. However, if there are 40 authors (from different time periods) all backing each other up, it seems much more credible and valid.