Part of my skepticism with regard to the efforts of my fellow atheists to demonstrate how absurd the opposing position is comes from knowing a fair number of intelligent, reasonable, thoughtful people who believe in God--including one I am married to.*Friedman's post talks about more than just the argument from expertise, but I'll leave his other points for later.
Stephen Law notes the weakness of the trope "Many leading philosophers are [religious] believers, so it can't be that unreasonable, can it?"
The argument from expertise as a justification for a belief is always a fallacy. If you agree with an expert about an issue without understanding her argument, then you are not really agreeing, because you don't understand what the expert is saying. Whereas if you do understand the expert's argument, then you agree with her on the basis of the argument itself, not her expertise. What one believes is inexorably bound up in how one believes it, because the arguments in favor of a proposition serve as part of the definition of that proposition.
An individual proposition doesn't have meaning on its own; a proposition always has meaning relative to some linguistic or theoretical context, and the justification of the proposition is part of that context. You cannot understand a proposition without understanding its context, including its justification.
Expertise as a fallacious justification for belief is different from expertise as a sound rational justification for action. I don't have to understand how my engine works to rationally justify paying my mechanic $1,000 to fix it. I neither believe her nor disbelieve her when she tells me the framistam is fershluggener. I don't understand her, and I don't care that I don't understand her. All I care about is that after I pay her $1,000, I'll be able to drive my car to work.
Expertise, though, is a poor basis for justifying even action. I don't really care where or even whether my mechanic went to school, and — since I don't understand engines — I have no way of judging directly how well she understands engines. What I do understand, though, is the reliability of the outcome. Regardless of what she does, whether she performs a scientific diagnosis or psychically heals the framistam with woo-woo crystal power, I can still evaluate directly whether or not I can drive the car to work when she's done. I don't really want her degrees and certifications; I want, rather, a guarantee: if I can't drive the car to work when she's done, I want my money back. Any useful indirect method of measuring "expertise" is really a method of measuring reliability, in terms I can understand.
When it comes to fields where reliability can't be measured at all — theology, philosophy, literary criticism — or fields where you can't measure reliability in a practical way — e.g. theoretical physics, the argument from expertise becomes entirely vapid. When you can't measure reliability, expertise has little utility. You either have to dig in and look at the arguments directly, or you have to profess pure agnosticism, regardless of the opinion of the experts.
Looking at the arguments directly, though, is not as hard as it seems. Most of the training that soi disant experts receive is focused on affording the ability to do original work in the field. But I don't have to be capable of doing original work to understand an argument, just as I don't have to be a concert pianist to appreciate Horowitz. I have a pretty good grasp of Quantum Mechanics, for example, even though I don't have a PhD in physics. I can't even contemplate doing original work in physics, but I can follow a physicist's argument for a concept, and thereby understand it directly.
Without appeal to the underlying arguments, I would have no way of even understanding, much less believing, a physicist when she says, "Light is both a particle and a wave."
I think expertise, especially without a corresponding notion of comprehensible reliability, has a corrosive effect on society. It's become too easy for someone to grind through a PhD program and then spout whatever bullshit he pleases. George W. Bush, for example, has a Master's degree — in Business Administration — and the guy can't operate a lemonade stand at a profit, much less the United States.