25,000 Christian Sects?

Yglesias and RBC have useful posts up about John Hagee, the fire-breathing San Antonio preacher who has endorsed John McCain. Extra points to Yglesias for situating Hagee’s much-touted “support” for Israel:

He argues that a strike against Iran will cause Arab nations to unite under Russia's leadership, as outlined in chapters 38 and 39 of the Book of Ezekiel, leading to an “inferno [that] will explode across the Middle East, plunging the world toward Armageddon.” During his appearance on Hinn's program at the end of last March, for example, the host enthused, “We are living in the last days. These are the most exciting days in church history,” but then went on to add, “We are facing now [the] most dangerous moment for America.” At one point, Hinn clapped his hands in delight and shouted, “Yes! Glory!” and then urged his viewers to donate money faster because he is running out of time to preach the gospel.

[“Hinn” is faith healer and televangelist Benny Hinn.] RBC remarks on how successful Christian politics has proven to be at bringing together “Christians” who are, historically, blood enemies (link).

All this reminded me of the assertion that there are 25,000 (or 22,000) Christian sects in the world, and to wonder whether they are all sending each other to hell, and if not, why not (Isn’t truth unique? Isn’t error error?). But wait—on what authority do I claim such multiplicity? Google “25,000 Christians” or “22,000 Christians” and you come up with plenty of hits, but no real baseline. The number—either one—actually sounds plausible to me, but is there any truth behind it, or are we all just making this up?