We find exactly the opposite to be true. If you were to go to an unknown area, would you want a map of the area? Well that is exactly what the LOI is: a map of the major deal points. In today's busy world it is important to be sure two parties are going down the same road and in the same direction before spending too much time working out all the details of a transaction.
There are enough litigation examples on this issue around to suggest their fears are well placed. A confidentiality agreement (also called a non_disclosure agreement) and followed by a letter of intent is the two step process for allowing a business concept owner to establish a new business relationship without losing control of their business idea.