Who was really underneath those black masks violent protestors wore during the 1999 WTO riots in Seattle? The founder of the Rainforest Action Network Randy Hayes thinks they may have been Seattle police.
At the Tulane Law School Summit on Environmental Law & Policy  earlier this year, Hayes spoke about the role of civil disobedience in promoting environmental causes. In defending civil disobedience, which he called a form of “compassion” and "respectful disagreement," he said masked violent protestors in Seattle may have been the police themselves. He said
I have friends who saw several people get out of police cars dressed as anarchists with the black mask and run over to a friggin' Starbucks or something and start smashing windows. So you tell me what gets reported in the press and what to believe. It's not always easy to tell.
His full presentation can be seen at the link at the bottom of this post.
The Rainforest Action Network and other partner organizations still point admiringly to the Seattle WTO riots as a "case study." The Rainforest Action Network even calls it "A Day to Remember." 
Additionally, Brent Blackwelder  the moderator of the panel that included Hayes, promoted a book called "Beautiful Trouble," which is a "toolbox for Revolution" (in the video you can see the web link on the white board behind Hayes). The Beautiful Trouble web page  encourages groups to "use your radical fringe to shift the Overton window." Rather than denouncing violent extremists, environmental activists see them as a useful tool in advancing their own political efforts.
Unfortunately, this is what passes as thoughtful environmentalism for many on the left.
You can watch the entire panel, including my arguments against self-indulgent civil disobedience, here .