So far as I am concerned, the government has no business knowing why and where I am traveling, what I am carrying unless it is harmful to those around me, or even who I am when I am traveling. It is an invasion of privacy to demand an answer to these things.
Then definitely don't leave the country. Some government employee will ask upon return.
Heck - even with domestic travel there are different inspection. I had a USDA inspection of a carryon bag when I left Hawaii. Upon entering California there may be border inspection stations. It's considered voluntary, but failure to comply can result in a vehicle being denied entry. The system has been in place since the 1920s and has survived Constitutional muster.
Since I spent the most part of 17 years working outside the country, I had noticed that. During that time, I was in and out between once and twice a year, and had probably about the same number of boder crossing between other countries, except for one period of two years where on average I made a round trip between Hong Kong and Taiwan on average about every 3 weeks. And, in that time, I will have to say that the least professional, least consistent, and in many ways also the least proficient customs inspection has been that of the US. One of my high points in silly questions was once coming in through Seattle, I think it was, being asked by they guy who was holding my US passport in hand, "Why are you entering the United States?" I am thinking, what is the trick here? while giving him the straight and simple answer.
Since the Hawaii - California inspections are related to plant diseases and parisites, I tend to regard these as legitimate. After all, the point is to control the movement of pests, not of persons. You dump the non-allowed substances and you are on your way.