I think the Jedi concept as explained by Obi Wan in ANH works well on a personal level. E.g., if a Jedi sees a man exploiting his workers or beating the helpless, he will intervene. Through strength of character the Jedi will see what is "right".
However, this concept does not hold up so well when applied to nations or planets. In TPM Qui-Jon and Obi-wan are sent to Naboo to "mediate" with the Trade Federation. But what "mediating" can they really do? What authority do they have to grant concessions for one side of the other? I think their only option would have been to get all the parties together for a peace tolk, where again, their supposed training in diplomacy and strong moral compass should see that everyone was dealt with fairly.
However, Lucas lost sight of what a Jedi should be and instead turned them into assassins and enforcers, understandable since every video game featuring Jedi has them mowing down any who oppose them and the movies are supposed to be action films. Still, I wish the Jedi counsil would have been better explained and shown in a more competent light.