Quoting is also an indirect way to get some idea on the table without having the responsibility of owning the idea...because it was someone else's idea, not yours, you cannot be attacked, blamed for it, made to answer a question about it, made to follow up on it - all of the attachment implied to having birthed the idea yourself...the same with quoting the historic authorship of the idea. The advantage is you can just dump it if the idea is not well-received by the group. The disadvantage is you may be asked for a book report. Then there's the advantage that you have been the source of the idea by being such a good reader and having the ability to trot out an adequate synopsis. But the disadvantage for the group is that nobody else may answer you, except with another quote that is somehow related.
So if more than one person does this, it very easily becomes an extension of the "who do you know" game.
I think the assumption behind this quoting thing, as well as the "no persona" idea is that the Freudian ego is the source of trouble. If you claim an idea as a product of your own thinking, observation or experience, it implies you "must" have a vested interest in the outcome of the conversation and this attachment is somehow forbidden. It's tricky to demonstrate that you do not have attachment to an idea that is your original one.
I think the reason people like to do this is they imagine that a lack of ownership or authorship is a sign of suspension by a willingness to dispense with any claim of authorship for original thinking.
Good think Bohm didn't impose that limitation on his own thinking!