Because it is the national interest of the US to allow Muslins to come here if they aren't terrorists. Why write off 1/5 of the world and also damage the US's reputation abroad by having a religiously discriminatory immigration policy?
If all Muslims are banned, the message will be clear and you won't see any talented immigrants come here, with the possible exception of European ones. Talented immigrants can enter virtually any country on Earth. They won't go anywhere that discriminates. President Bush has the right policy on legal immigration.
Because "moderate Moslems" are as rare as unicorns. They almost universally SUPPORT the goals of terrorists. They belong to organizations like Hamas that promote terrorism. We didn't let Nazis in. Why should we allow Islamo-fascists?
"If all Muslims are banned, the message will be clear and you won't see any talented immigrants come here, with the possible exception of European ones."
You're right. The Indians, Chinese, Japanese, Koreans, etc. have all said they'll only come to America if we let their muslim friends come too. Why just yesterday I was speaking to a Sudanese animist who said that even though his village was recently overrun and his grandma was set on fire by the janjaweed, he still thinks it would be wrong of America to exclude muslims. Afterall, they don't discriminate; when they kill people, they make sure to include everyone.