Sure. And treat all visitors like criminals right off the mark. Nice welcome.
It's not treating anyone like criminals. It's recognizing that there ARE going to be criminals out there, and trying to sort them out.
One point is to make sure that the individual, presenting a visa, is the same person who was issued the visa overseas. This, contrary to what Peg said, is preventative in nature.
It is true that this will not solve all problems, but then no measure that could be taken will solve all problems. You attack a problem by doing what can presently be done, and later try to stop up the other holes. And no set of security measures will ever give absolute protection, but that doesn't mean that the country should throw up its hands, roll its eyes, and give up.