Then why do we allow people to edit articles at all. Under strict risk/reward analysis, that was the wrong thing to do. Yet by doing the "wrong thing" we have created something quite significant. In my opinion, your assessment of risk/reward is more appropriate to a well-established institution than to a cutting-edge web project.
In what way was it the wrong thing to do? The gain from allowing everyone to edit is enormous. The risk is significant, but manageable.
All decisions should be made by comparing the risk and the reward. The difference between a well-established institution and a cutting-edge web project is simply one of degree - we are willing to take more risk to get the same gain, but no unlimited risk. We still have to balance it.