The Washington Post has a great piece up written by a man that is banned from the United States even though the State Department can't state a reason why. The author speculates that it has a lot to do with his outspoken criticism of US foreign policy.
For more than two years now, the U.S. government has barred me from entering the United States to pursue an academic career. The reasons have changed over time, and have evolved from defamatory to absurd, but the effect has remained the same: I've been kept out.
First, I was told that I could not enter the country because I had endorsed terrorism and violated the USA Patriot Act. It took a lawsuit for the government eventually to abandon this baseless accusation. Later, I reapplied for a visa, twice, only to hear nothing for more than a year. Finally, just 10 days ago, after a federal judge forced the State Department to reconsider my application, U.S. authorities offered a new rationale for turning me away: Between 1998 and 2002, I had contributed small sums of money to a French charity supporting humanitarian work in the Palestinian territories.