Once upon a time, the The Nature Conservancy and EDF were the only environmental groups I contributed to. The economist in me liked TNCs narrow mission of buying conservation land, and EDF was the most economically savvy of the big environmental groups.
Since then, TNCs simple mission to acquire private nature preserves became mired in political advocacy, using public money, insider land deals, and questionable ethics (of course, they got bigger, more influential and richer with the change in mission). Like many others who stopped donating back in 2003, I never came back (not that they miss my modest membership fee). They made public apologies, and created new ethics guidelines in 2004, but I wasn't convinced.
To my knowledge, this is the only environmental group ever to have Senate hearings regarding their ethics. If you are unfamiliar with the history, I recommend a series of articles by Stephens and Ottaway in the Washington Post around 2003.
This article in today's Sacramento Bee reminds me why I quit.