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.
Confidentiality Agreement. A confidentiality agreement is a "first date" agreement.. Often the two parties have had little business dealings with each other prior and the purpose of the discussions is to determine whether there is a mutual interest in what is being discussed. Note however that it is just as necessary to have a confidentiality agreement when the parties know each other well. Discussions under confidentiality allow the information receiving party to stay "Stop, let's not take this discussion further as I am already doing what you are disclosing to me".