Your understanding of NDAs generally aligns with common legal principles. Non-Disclosure Agreements (NDAs) are legal contracts designed to protect confidential information. They are often used in business settings to safeguard proprietary information, trade secrets, or other confidential matters. However, the enforceability and limitations of NDAs can vary based on jurisdiction and the specific terms outlined in the agreement.

Here are some general points based on your statements:

1. Legitimate Use of NDAs:
   NDAs are typically intended to protect legitimate business interests, such as intellectual property, trade secrets, and confidential information. Misusing NDAs to suppress information about criminal activities may not be legally enforceable.

2. Criminal Offenses vs. Embarrassing Information:
   NDAs are not generally designed to prevent individuals from testifying about criminal offenses. If an NDA attempts to cover up illegal activities, it may not hold up in court, and individuals may still be able to speak out.

3. Defamation:
   Defamation is a separate legal concept from NDAs. NDAs focus on confidentiality, while defamation involves making false statements that harm someone's reputation. Truth is often a defense against defamation claims.

4. Enforcement and Penalties:
   The enforceability of NDAs depends on the specific terms, jurisdiction, and the nature of the information involved. Penalties for violating an NDA can include financial damages, injunctions, or other remedies specified in the agreement.

5. Post-Employment Restrictions:
   NDAs may include provisions that extend beyond the termination of employment, but their enforceability can be subject to legal scrutiny. Post-employment restrictions need to be reasonable in scope, time, and geographic reach to be enforceable.

6. Psychological Impact:
   NDAs may indeed have a psychological impact on individuals, often influencing their behavior even after leaving a company. However, the enforceability of NDAs is a legal matter, and individuals should seek legal advice if they have concerns.

It's crucial to consult with a legal professional for advice tailored to specific circumstances and jurisdictions. Laws can vary, and legal advice should be sought for any situation involving NDAs or related legal matters.