Plagiarism is the author's attempt to use the work of other people as your own, without disclosing their involvement. Astroturfing is exactly the oppose: it is an organization's attempt to attribute their own work to other people without disclosing the involvement of the organization.
If I said Paul Krugman was a plagiarist because he quoted other people in his columns (with attribution), that would be ridiculous. I would owe him a correction. And possibly monetary damages. Words mean things.
Yet, in today's New York Times column (in which he makes some reasonable points about the sad state of the Republican Party), Paul Krugman grossly misuses a term to libel a variety of people.
Last but not least: it turns out that the tea parties don’t represent a spontaneous outpouring of public sentiment. They’re AstroTurf (fake grass roots) events, manufactured by the usual suspects. In particular, a key role is being played by FreedomWorks, an organization run by Richard Armey, the former House majority leader, and supported by the usual group of right-wing billionaires. And the parties are, of course, being promoted heavily by Fox News.
What Freedomworks and various other organizations are doing is not "astroturf" any more than the anti-war protests of some years back were astroturf because ANSWER and Moveon.org helped organize people around those events. Astroturfing is paid activism by an organization; it is not genuine grassroots activism that funded groups are simply helping to organize.
The Center for American Progress & Think Progress, of all groups, should know better than to use the word "astroturf" against funded, ideological 501c(4) organizations that are trying to organize activists. Especially considering how many funded, ideological 501c(4) organizations they have trying to organize activists.
The accusations Paul Krugman makes in the New York Times are very similar to the talking points that have spontaneously arisen in the Leftosphere recently, and their attempts to delegitimize these policy protests are not likely to stop unless the Right fights back. For starters, unless Krugman and the New York Times issue a correction, the people they have libeled should consider responding to this libel through appropriate legal channels.
Beyond that, it is crucial that the groups attempting to organize activists around these Tea Party protests see their role as service-oriented infrastructure. Provide the information and tools, and let the grassroots continue to organize themselves.
UPDATE: Contra Matt Yglesias, I did not "attack CAP/AF as astroturf". Indeed, my point was that the CAPAF (Think Progress) "grassroots advertising and organizing" is not astroturf, so they shouldn't throw the astroturf accusation at other groups that do grassroots organizing.
For the record, astroturf really requires two things: (1) A claim to be organic/grassroots, and (2) non-disclosure of the non-grassroots group that is really behind the activity. Organizational involvement in activism is not, itself, astroturf. Nor is it astroturf when an organization conducts its own activism project with full disclosure of their involvement.