The John Birch Society never called Fluoride in the Drinking Water a "Communist Plot," that was Leftist propaganda.
Youtube:
John Birch Society: Fluoride in the Drinking Water, Official Statementhttps://www.youtube.com/watch?v=sZ7AyB2kFng
Also here:
John Birch Society: Myths vs Facts
Myth: The JBS considers public water fluoridation part of a Communist mind-control plot.
Fact: While the JBS doesn't agree with water fluoridation because it is a form of government mass medication of citizens in violation of their individual right to choose which medicines they ingest, it was never opposed as a mind-control plot. If citizens want to add fluoride to their diet or daily routine, there are plentiful opportunities for them to do so. It’s a choice they should make, not their local government. Furthermore, opposition to fluoridation was never a major action item of any JBS campaign.