It is just a legal gimic to pile on additional charges should a visitor to the USA be caught conducting terrorist actions. The same strategy is in narcotics. Did you know if you sell illegal narcotics your suppose to buy tax stamps?
http://www.ksrevenue.org/perstaxtypesdrug.htm
http://talkleft.com/new_archives/009164.html
http://ezinearticles.com/?Truly-Biza...s&id=39479
Most criminals are smart enough to know that by buying these tax stamps they increase their chance of being caught so they don't buy them. If they do get caught, now they face tax penalties where their assets can "legally" be seized.
Anyway, there is a reason for putting these types of questions on Visa forms...