I'm not repeating this in every comment because it feels tiresome, but, like I said, I'm glad this guy is out there pushing the frontiers of our civil liberties, but I still think he's a bit of a douche, and I still think his arguments don't make much sense: his fear of the consequences of answering "business or pleasure" seems irrational compared to the powers the border police already have to search his luggage, the files on his computer, and his body cavities without a warrant.
Incidentally, the principled stand this guy took for not answering questions seems a bit hollow when you consider that, semiotically speaking, he pretty much answered their question: "yes", he said, "I am very much worth your time to scrutinize further."
Consider how comfortable a person is when speaking to a telemarketer compared to a police officer or border patrol officer.
That we must grovel before those in uniform is a clear sign that they have too much power.
Of course his behavior was irrational if he was someone trying to smuggle in contraband. But it was rational if he's someone who feels that his rights as a law abiding citizen have been compromised by the re-entry procedures and seeks to make a point.