The usefulness of wikipedia as a repository of human knowledge suffers greatly from the current restriction to mainstream views only. There is more knowledge in the alternatives than in the entrenched views, so wikipedia gets to present less than half the available knowledge.

Whether something has been published elsewhere or is in accord with received wisdom should really not be a criterium for allowing publication. What’s wrong with a note saying that “this is not from published scientific sources”, somewhat akin to “this statement has not been evaluated by the FDA” which we sometimes find on food labels.

Banning is only the tip of the iceberg of a much more serious and potentially disastrous situation at wikipedia, which is the exclusion of new knowledge.