Would you answer honestly if a national crime survey asked you about your criminal behavior, including drinking and drug use? if not, why not? if you would not answer honestly, do you question the accuracy of self-report surveys?

If I was an alcohol or drug user, I  would probably lie and not mention that I am a user. I would lie in order to "save face", not look like an immoral person and avoid negative judgement from the researcher. Yes, self-report surveys are not always valid because it is common for participants to lie, forget or omit mentioning relevant information in their responses so that they come across as socially desirable.