There's some clear anger under that mockery. Smith considers himself a reasonably even-handed news anchor there -- I can't imagine he's too thrilled by the prospect of promoting Beck who is a parody of a satire of a cartoon of a far-right cable news pundit. With a punch-me face.
UPDATE: From Chez Pazienza in the comments:
I worked closely with Shep in Miami and we were poker buddies in L.A. I consider him a good friend. He's a really great guy with a very level head -- not real big on bullshit. Which would make me wonder what he's doing at Fox if it weren't for the fact that he knows which side his bread is buttered on and is enjoying that really nice paycheck they're giving him. As much as Fox is a joke of a network, it's kind of good to have Shep there to highlight the place's bombastic insanity from the inside out simply by being the slyly subversive voice of reason.
Shep is definitely a fair-minded anchor trapped in an ocean of crazy. Here's one of my favorite Shep Smith moments. And here's Shep nailing Joe the Plumber.