For one thing, I do not spend my vacations at a terrorist training camp in Pakistan.
For another thing, my son WAS held up at the border for several hours because his (non-U.S.-national) wife's visa was expired.
Eventually they were allowed into the country because they have no terrorist connections.
If an FBI guy wanted to interrogate you, say, just for practice, he could have you committing a Federal Offense - lying to an FBI agent -- in about five minutes. It is the simplest thing in the world. It would make absolutely no different who you were, or what you were, or how you had lived your life.
First he would make you nervous, if you were not already nervous. Then he would make you confused, then when you made a verbal slip, he would work you over on it, till you answered SOME question two different ways. Or he would go back and question you on some obscure point you made earlier, hoping you would answer it somewhat differently. Obviously, one of the ways would have to be false. Presto - you've lied to a Federal Officer, and it's off to jail you go.
Take, for example, your statement ""I do not spend my vacations at a terrorist training camp in Pakistan"
He might ask so, the training camp was in Afghanistan, then? Or are you saying you were not on "vacation". How DID you get the time to attend that terrorist camp, then? See, he could take that statement and show how it's consistent with an admission that you are a terrorist. Pretty nasty, huh? Not the least bit sporting. That's why the FBI wants to make sure you talk without a lawyer present. Because you will wind up admitting whatever words they want to put in your mouth.
I, too, have been held up at the border, because my wife [not yet a permanent resident or citizen at that point] needed to have her fully valid and regularly issued "advance parole" document further processed, which is normal procedure, but I was not aware that the further processing would be necessary. The processing took about 20 minutes, which was enough to cause us to miss our connection. Unlike your son and his wife, our papers were completely in order, but we were held up anyway.
This occurred in Toronto, which is where you clear immigration on flights coming in from Canada, and caused us to miss our connection, and have to spend the night in Toronto. I was kind of steamed, which made my interchange with the immigration official a bit testy at first, particulary when I started writing down names, because I did not know what other suprises might be in store for us, and I wanted a record of what happened.
At the end of the interview, when our paperwork was signed off, and I had calmed down, the officer asked me if I had any complaints. He asked this question three times, in three different ways. The reason, of course, is that we were being videotaped and audiotaped, and he was covering his posterior in case I complained later.