Via Instapundit, I have my answer:
I've walked away from arguments feeling frustrated in the past, with the vague feeling that I didn't present myself or my arguments well. That's because I'm always willing to admit the possibility that I'm wrong.
But Glenn has faith, an unshakeable belief that his core values are right. That sounds unreasonable to me, but it's also something that has been the sole domain of the Left until recently. Glenn's faith empowers him as it does those who "speak truth to power," and it scares the bejesus out of them.
Once, long ago, I read Robert Heinleins Job: A Comedy of Justice. It made me re-examine a lot of things I had taken for granted about the world around me. And I promised to never give that book to someone with a strongly expressed faith, because it made me doubt and ask questions. I don't regret it, but life was so much more complicated after that.
Perhaps I was wrong. Perhaps more people should question their ideals. Regardless, it's that faith and conviction that wins the day, and Beck has it, and more people on the right are following his example. This is a real concern for those who thought they had a lock on moral outrage.