"I fear the man of one book" - What is your attitude towards this thought?

Excellent question. I share your surprise at the bookish approach of some Buddhists.

We should definitely fear the man of one book, or fear for him. The man of no book would be in a much better position. Even the ancient Rig Veda is critical of 'people of the book' and warns us to watch out and avoid them.

But it may depend. Buddhist have not a book but a vast literature and these days it covers most topics and areas of study. So perhaps the man of one literature is not always to be feared. There is also the kind of book that does not need not be duplicated, for instance a single book that explains Newton's' laws of motion might be enough for many people.

Certainly I would fear any religious believer who trusts only one book and ignores the rest. What you say about the way the Dhamma is discussed seems fair, but scholarly discussions may depend on analysis, some of which may be found in books, and this is a sensible topic to discuss. It's when what is said in books is used to replace logic and experience that the alarm bells go off and discussions take on a sectarian and even pantomime quality.

I read and agree with your statement as appropriate and insightful. The statement appears to match your experience, my experience and the Buddha confirms this as:

There are two conditions for the arising of right view: the words of another and proper attention. --MN43

I'm sure we could find more people and works that agree with title of this post. However I'm not sure that truth should be validated by number of believers. We have, for example at one time thought the world flat. The fact that you, I and the Buddha agree seems good and enough.

You can study other fields like science, psychology, philosophy, physiology, culture, other religions etc. That's no conflict with Buddhism.

However, using other fields to validate Buddhism is not the right approach. The reason for this is that other fields have different objectives compared to Buddhism. To compare them would be the same as comparing oranges and apples.

Buddhism has one primary objective - to reduce and end suffering, which basically relates to achieving permanent stable happiness.

The only way to validate Buddhism is to compare its teachings and the effects of its practices (as practised by oneself) against one's own experiences. Does it reduce your suffering? Does it help you reduce your bad habits and improve your harmony with yourself and others? Does it promote an increase in your own happiness and better psychological well-being?

Back to the first point, studying other fields can broaden your understanding of other fields. This has a few benefits.

Firstly, it helps prevent a Buddhist from becoming extreme or ritualistic or overly clinging to rules in his view. This actually is one of the fetters that the stream winner has to eliminate, through seeing the Dhamma clearly.

Secondly, it prevents a Buddhist from becoming disconnected from the "rest of the world". The Buddha wanted his monks to depend on the laity for alms, so that the monks don't become disconnected from the "rest of the world" and also for the laity to interact and learn from the monks.

Thirdly, understanding other fields can help with the validation of Buddhism against one's own experiences, because it can help feed one's insight. Let me use the example of Nobel prize winning physicist Richard Feynman (quoted below from here). Teaching basic physics to students is not required for one dedicated to research, but getting questions and interacting with students help to feed into his insight, so he found it necessary.

So, although Buddhist teachings and practices combined with one's own experience is enough to "research" (i.e. gain insight) into the nature of one's reality in order to end suffering, learning other fields can be helpful in feeding that insight. In this question, I tried to compare the nature of the mind vs. body to software vs. hardware. That doesn't mean mind IS software, but knowledge of the nature of software vs. hardware can feed into the insight into the nature of the reality of mind vs. body.

When I was at Princeton in the 1940s I could see what happened to those great minds at the Institute for Advanced Study, who had been specially selected for their tremendous brains and were now given this opportunity to sit in this lovely house by the woods there, with no classes to teach, with no obligations whatsoever. These poor bastards could now sit and think clearly all by themselves, OK? So they don't get any ideas for a while: They have every opportunity to do something, and they are not getting any ideas. I believe that in a situation like this a kind of guilt or depression worms inside of you, and you begin to worry about not getting any ideas. And nothing happens. Still no ideas come.

Nothing happens because there's not enough real activity and challenge: You're not in contact with the experimental guys. You don't have to think how to answer questions from the students. Nothing!

In any thinking process there are moments when everything is going good and you've got wonderful ideas. Teaching is an interruption, and so it's the greatest pain in the neck in the world. And then there are the longer period of time when not much is coming to you. You're not getting any ideas, and if you're doing nothing at all, it drives you nuts! You can't even say "I'm teaching my class."

If you're teaching a class, you can think about the elementary things that you know very well. These things are kind of fun and delightful. It doesn't do any harm to think them over again. Is there a better way to present them? The elementary things are easy to think about; if you can't think of a new thought, no harm done; what you thought about it before is good enough for the class. If you do think of something new, you're rather pleased that you have a new way of looking at it.

The questions of the students are often the source of new research. They often ask profound questions that I've thought about at times and then given up on, so to speak, for a while. It wouldn't do me any harm to think about them again and see if I can go any further now. The students may not be able to see the thing I want to answer, or the subtleties I want to think about, but they remind me of a problem by asking questions in the neighborhood of that problem. It's not so easy to remind yourself of these things.

So I find that teaching and the students keep life going, and I would never accept any position in which somebody has invented a happy situation for me where I don't have to teach. Never.