In today's Washington Post, Andrew Sullivan has a powerful op-ed about a U.S. immigration policy I didn't know existed: a ban on visitors who are HIV-positive. You really should read the whole thing, but here's just an excerpt:

  Twelve countries ban HIV-positive visitors, nonimmigrants and immigrants from their territory: Armenia, Brunei, Iraq, Libya, Moldova, Oman, Qatar, the Russian Federation, Saudi Arabia, South Korea, Sudan and . . . the United States. China recently acted to remove its ban on HIV-positive visitors because it feared embarrassment ahead of the Olympics. But America's ban remains.
  . . .
  The ban can be traced to the panic that dominated discussion of the human immunodeficiency virus two decades ago. The ban was the brainchild of Sen. Jesse Helms (who came to regret his initial hostility toward people with HIV and AIDS). President George H.W. Bush sought to drop the ban, but in 1993, after a scare about Haitian refugees, Congress wrote it into law.
  I remember that year particularly because it was when I, a legal immigrant, became infected. With great lawyers, a rare O visa (granted to individuals in the arts and sciences), a government-granted HIV waiver and thousands of dollars in legal fees, I have managed to stay in the United States. Nonetheless, because I am HIV-positive, I am not eligible to become a permanent resident. Each year I have to leave the country and reapply for an HIV waiver to reenter. I have lived in the United States for almost a quarter-century, have paid taxes, gotten married and built a life here -- but because of HIV, I am always vulnerable to being forced to leave for good. After a while, the stress of such insecurity gnaws away at your family and health.
  This law has lasted so long because no domestic constituency lobbies for its repeal. Immigrants or visitors with HIV are often too afraid to speak up. The ban itself is also largely unenforceable -- it's impossible to take blood from all those coming to America, hold them until the results come through and then deport those who test positive. Enforcement occurs primarily when immigrants volunteer their HIV status -- as I have -- or apply for permanent residence. The result is not any actual prevention of HIV coming into the United States but discrimination against otherwise legal immigrants who are HIV-positive.
  People with HIV are no less worthy of being citizens of the United States than anyone else. All we ask is to be able to visit, live and work in America and, for some of us, to realize our dream of becoming Americans -- whether we are HIV-positive or not.

  As I said, I didn't know this ban existed; now that I know of it, it sounds absurd. Unless there's some counterargument that I can't think of right now, it seems like a slam dunk that Congress should pass legislation ending the ban.