Not as rare as you think, surviving Greenpeace co-founder Dr. Patrick Moore renounced them when the watermelons infested and subverted the movement, and the same thing happened to the Sierra Club. Moore now runs Greenspirt, advocates growing more trees, using the wood and supports Bjorn Lombard as well as denounces Scientific American.
Niether Greenpeace or Sierra Club started out as radical orgs, but were co-opted by the radical Marxist spawned in the 50's & 60's.
Typical lefty tactic, infiltrate, outnumber, then take over. Has happened to many of our organizations - the ACLU, many churches, our school system, the unions (although some unions started out that way), etc., etc. Ralph Nadar was an early pioneer, also.
Thanks for the information about Greenpeace and the Sierra Club.