I think there may be a blind spot over the term in the UK, but I suspect only among atheists. I've been racking my brain trying to see where using the word is not either a put down or a diagnosis.

He is deluded if he thinks she is going to go out with him.

She is deluded if she thinks french fries don't go to right to the hips.

Please explain to me how Mr. Dawkins title is not a put down. I think that if you are defending or excusing that title, you have a lot of balls to tell me, a thoughtful human being, that I have any kind of delusion whether it be a medical one or not.

Why don't you test it. Why don't you walk into a pub and yell out "Who here believes in God?" Go up to the biggest guy who says "yes", ideally one in a rugby shirt, and say. "I am sorry to inform you, but that have a delusion." Be as polite as you can but be firm about the fact of the delusion. Be careful to explain that you are not offering a medical diagnosis, just tell him that his beliefs are "something that is falsely or delusively believed or propagated." Or use any innocuous version of definition you want. See what happens.

Or what if I said...

Dawkins' followers were deluded. He has no scientific basis for his claim that has not been argued to death for 500 years and that from his actions he is clearly in it for the money. That he got famous because of his rampant Islamophobia and he is a hypocrite for not applying the same rigor to his own public statements as he does to statements from the pulpit.

All of those statements are debatable except possibly the first. But the first is not there to be debated. It is there to provoke. Dawkin's will get their ire up when they read it and it will color every other statement. Try it if you are inclined to scientific experiment. Send it in a private message to Mr. Shaw. His head will explode.

Send this to Musket, you will likely get a reasoned argument.

I believe that Dawkins' followers may be mistaken . He has no scientific basis for his claim that has not been argued to death for 500 years and that from his actions he is clearly in it for the money. That he got famous because of his rampant Islamophobia and he is a hypocrite for not applying the same rigor to his own public statements as he does to statements from the pulpit.

Delusion Etymology

delusion (n.) Look up delusion at Dictionary.com
    "act of misleading someone," early 15c.; as a form of mental derangement, 1550s, from Latin delusionem (nominative delusio) "a deceiving," noun of action from past participle stem of deludere (see delude).

So it started out meaning a form of mental derangement. When and how was it every used as either a diagnosis or a mocking put down. I invite you and the entire Mudcat to comb all of literature except of course for Mr. Dawkins book, to find an example where the word is used to describe a person or a group where it is not used in mocking or in pity or as a diagnosis.