How does calling someone an "idiot" make one bound for Gehenna? How does calling someone an "idiot" make one bound for Gehenna? I'm sure there is something of translation, meaning, or ancient culture to be considered here.


  ...and whoever says, You cursed fool! [You empty-headed idiot!] shall
  be liable to and unable to escape the hell (Gehenna) of fire.
  
  Matthew 5:22 (Amplified Bible)



Is this a point lost in translation? 
What point was Jesus making when he said this?
It's not so much something lost in translation, though there may be some cultural factors coming into play. Jews considered the Words of the ten commandments to be minimum requirements, and beginning with Matthew 5:21, Jesus expounds on some the commandments pertaining to the relationship to other other people. The essence of the teaching in Matthew 5:21 ff is that the actual commandment not to murder is insufficient. Not only is murdering another a violation of the commandment, but even to insult another person violates the spirit of it. He then similarly expounds on others of the commandments, for example, not only is it a sin to commit adultery, but it is a sin to think about committing adultery. After making similar comments on other commandments, Jesus summarizes his points in Matthew 5:48--"You, therefore, must be perfect as your heavenly Father is perfect." (RSV)

To go back to the original question, merely not committing murder is imperfect, as it is the minimum required. Not insulting another person, as in calling them a fool, is perfection.