Goku is not a coward... He just can't stand Sanzo being in danger... Sanzo is his life... his reason to live.... So he will risk anything to protect his precious sun... even turn a blood thirsty maniac....
@vanglak - really? I think he takes it off because he's too nice and the only way he'll kill is if he's in his real form. Nothing to do with strength. Kougaiji said he had to kill him, and for Sanzo he's willing to risk sanity.
the monkey king son goku the voices would very but they would naturaly stay the same..but being goku was chained to a rock for ..500 years...sealed in a human form..it would make since if he never changed..the monkey king is supposed tohave