My experience with the different aspects of confidentiality ranges from military/government, through corporate R&D (at IBM Research) and as an executive in the private sector (as CEO and founder of a tech company).
Of course, if the disclosure of any details could do harm for anyone outside yourself or your organization (as is the case in government applications) - then the information should not be disclosed.
If the information is an idea, my experience has been that people are too worried about sharing ideas. I've had many situations where I disclosed the details of my idea in full, to people who have the resources to compete with it against me if they wanted, and I have never had anyone do that. To make an idea reality you have a thorough mental image in your mind of what the final product would look like, and chances are only you have that image at the necessary level of detail.
Regarding specific product information (when it is not publicly available) or quantitative business data (like forecasts): I have always been very careful with those, and only disclosed after signing an NDA. I also viewed the disclosure as a point of no return in the relationship, and assessed how much I personally trust the person I share the information with.
I'd be glad to chat further and provide more input based on the specifics of your debate.