Well this is a classic case of showing rudeness and expecting nice behavior.
The OP in that thread indeed was rude to the CBP officer by replying "none of your business"; however, technically he was correct because asking why a returning citizen visited a particular country is none of their business. He could have started with "I refuse to answer irrelevant questions that don't pertain to admission into my own country", but I am sure it would land him in the secondary just as well.
I do acknowledge that many immigration officers/passport control officers can be rude, but there are many many which are very nice. I personally have seen both.
I have seen both too, but even the nicest ones still asked me bunch of quite personal questions (e.g., what work I do, what major I am studying, why I went to particular countries, etc). The bottom line is that a US citizen does not have to answer these questions to be admitted to his own country. The CBP knows it all too well, but they also have the power to refer you to the secondary just to show you that they can - so that you will be more "cooperative" next time.
What Jackolantern mentioned is that if the officer tries to play games to increase the fear factor. It doesn't mean that Jackolantern implies to be impolite or rude from the beginning.
That is irrelevant. When Jackolantern tries "to put officer in his place", he will most likely go to secondary regardless if he is nice or rude.
You also have to give some slack to those immigration officers. They are humans and have to deal with hundreds of people everyday. It could happen that he/she had to deal with a moron and was still in a bad mood when you got their.
This is irrelevant. Regardless of what mood a CBP officer is in, I expect him/her to do the border related functions, not ask me many personal questions and then see if I stumble on one of them.
Anyways, this is an endless debate. If someone is nice with me, good enough. If not, then I will remain nice because I do not want to go to the lower level of humanity.
There is no debate here. Being nice pays off only when the system is set up fairly. In case with CBP, it is not.