NDA's are extremely valuable and important. There are several different types of these agreements, so to generalize that they are detrimental overall is reaching at best. NDA's are always important in settlement issues because a settlement does not mean that the settling party accepts any culpability or liabilty. To avoid a rash of others to seek relief from the settling authority, and therefore cause that entity undue hardship, they are an important protection. But there are other reasons why they are imprtant.
First and most obviously, they protect sensitive technical or commercial information from disclosure to others. One or more participants in the agreement may promise to not disclose technical information received from the other party. If the information is revealed to another individual or company, the injured party has cause to claim a breach of contract and can seek injunctive and monetary damages. Second, the use of confidentiality agreements can prevent the forfeiture of valuable patent rights. Under U.S. law and in other countries as well, the public disclsure of an invention can be deemed as a forfeiture of patent rights in that invention. A properly drafted confidentiality agreement can avoid the undesired—and often unintentional—forfeiture of valuable patent rights.
Confidentiality agreements also define exactly what information can and cannot be disclosed. This is usually accomplished by specifically classifying the nondisclosible information as confidential or proprietary,amnd setting specific timlines, etc. There are several situations where a confidentiality agreement is appropriate and may be proposed, but I will admit that they are often times used too frequently, and there is a big push to see greater transparency, though I doubt they will ever go away really.