I think figures like Richard Dawkins can have positive effects, since they don't just tear down people's beliefs, but create alternative institutions like "The Richard Dawkins Foundation for Reason and Science." Same with The Infidel Guy.
That said, I think we all act on faith, as there's often little alternative. What counts is our honesty about it. Fortunately, we often compartmentalize parts of our lives, so my faiths in one area don't necessarily bleed much into others.
Speaking of that, anarchist philosopher Mark Lance mentioned a downside to this compartmentalization. He claims that successful revolutionary movements pretty much always resulted in societies which were massively less progressive (democratic, egalitarian) than the movements themselves which brought about the change. He doesn't know of a counterexample. Sometimes the post-revolutionary society is even regressive compared to the pre-revolutionary one.
"Well, what's going back to ordinary life? It's going back to the range of habits and skills things that you've had your whole life that you've gotten from living in an oppressive, capitalist, commodified authoritarian structure. and so I want to say we all are currently are a mass of authoritarian commodified capitalist skills. Even the people in this room who've been trying to fight that their whole lives." <http://ftp.radio4all.net/pub/archive/05.29.04/ug192-hour1mix.mp3>
So I think that people are very correct in being suspicious of the highly developed belief systems we often see within the left and anarchism.
Tayssir