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It's a small jump from stealing ideas to stealing text.
Stealing ideas is also plagiarism, and unethical.
In the example you provide, though, Jeff Greenwald cites a February article (http://www.nytimes.com/2009/03/01/opinion/01dowd.html?ref=opinion) in which Dowd equates Obama with Spock. She did not steal his idea in her article this month and he didn't steal hers:
Spock has been on many minds lately, and not entirely because of the new film. Big thinkers in both print media and the blogosphere -- from New York Times columnist Maureen Dowd to MIT media moguls -- have referenced the Enterprise's science officer in recent months, drawing parallels between the dependably logical half-Vulcan and another mixed-race icon: Barack Obama.