As the other guy mentioned, devolving into 4chan, tumblr and reddit are what happens when there is no individual cost--disincentive, not necessarily financial--to polluting the public information pool. The first layer of defense is a scarce publishing profile, the second is scarce publishing frequency and third is individual accountability.

There are very few scenarios where a person can be physically threatened by the nature of their information. In those rare situations, anonymity doesn't protect the individual because the information is likely only privilege to a small group.

To identify content of public importance, you would need to identify which people the information is important to geographically and then determine the demand via market forces and then determine the trustworthiness of the content by evaluating the individual sharing the information.

You end up with a trust structure tied to publishing capability on a geospatial information system.

Already building it!