Herewith, two scenarios.
Scenario A: The supposedly inept president of the United States carefully planned and orchestrated the worst terrorist attack on American soil in our history. Though "only" 3,000 people died, the plan was to kill many more by simultaneously attacking the World Trade Center, the Pentagon and either the U.S. Capitol or the White House itself on Sept. 11, 2001.
Hundreds of people, including personnel from myriad agencies, participated. According to some versions of Scenario A, explosives were placed at the World Trade Center to ensure success. In other versions, all of "the Jews" working there were tipped off by some phone bank run by the Mossad. In every version, however, the U.S. government was in on it, and everyone involved kept the biggest secret in American history.
Then, there's Scenario B: An ambitious and extremely clever politician, who has at best been selectively forthcoming about large chunks of his youth, lied about his place of birth so he could be eligible for the presidency.
To further this scheme, he has arranged for the full and/or original version of his birth certificate to remain under lock and key. At most, a handful of supporters and lawyers are in on the whole thing.
Now, which one is more believable? For the record, I don't believe either. But it seems to me the "birther" hypothesis is vastly more plausible than the "truther" hypothesis. Politicians lie to advance their careers. You can look it up. Whole governments rarely orchestrate incredibly complex acts of physics, logistics and mass murder all the while pinning guilt on others (who boast that they acted alone).
Just for clarification: "Truthers" believe scenario A. "Birthers" believe scenario B.
The question of which scenario is more plausible is neither academic nor trivial. This summer, a host of columnists, commentators and activists, seemingly taking their cues from a White House and DNC public-relations offensive, declared that the rise of the "birthers" was a fatal indictment of modern conservatism and the Republican Party. The refusal of the birthers to give up their cockamamie theory was proof that the GOP had succumbed to the "paranoid style." Indeed, according to some liberal commentators the birthers were the potential wellspring for a nascent Nazi movement in America. Never mind that the vast majority of leading Republicans and conservatives -- from Newt Gingrich to Ann Coulter -- rejected the birthers categorically.