It depends on what other limits they place on the use of the town facebook page. If they consistently apply the rule that only content related to the monthly p

It depends on what other limits they place on the use of the town facebook page. If they consistently apply the rule that only content related to the monthly potluck is allowed, then they would be allowed to block PETA (this is similar to the example the article gives of a public library that hosts a discussion board exclusively for book recommendations). They wouldn't be able to block someone who complained that the food would at the last potluck was bad, because that would be blocking them based on viewpoint rather than based on topic.