I did not watch the Glen Beck rally but have read the analysis of others, including Russell Moore. He notes how far we (evangelicals) have fallen in the last thirty years: "It’s taken us a long time to get here, in this plummet from Francis Schaeffer to Glenn Beck. In order to be this gullible, American Christians have had to endure years of vacuous talk about undefined “revival” and “turning America back to God” that was less about anything uniquely Christian than about, at best, a generically theistic civil religion and, at worst, some partisan political movement." That's one side of the coin.
Gene Veith shows us the other side of that coin - a Mormon's view of the rally. In short what the Mormons got out of the rally was legitmacy. They now believe that the they have been embraced by evangelicals as Bible-believing Christians.
I'm astonished that evangelicals now rally around a Mormon as their leader. What happened to Schaeffer's distinction of "co-belligerency"? Where is the basic understanding of Mormonism that it has a defective view of Jesus Christ (i.e. not in keeping with the Nicene or Athanasian Creeds)? I believe that this is the fruit of thirty years of church growth, topical sermons, and "practical", consumer-oriented Christianity. I shudder to think where we will be thirty years from now.
Veith also has a link to David Barton's explanation as to why he supports Glenn Beck. I've never had much use for his work and this statement is the final nail in that coffin.