Almost all of them are overseas, outside of US territory and jurisdiction.

http://en.wikipedia.org/wiki/Black_site#Suspected_black_site...

Didn't you hear of these suspected terrorists sent by the CIA to Morocco, Syria or elsewhere explicitly to be tortured?

Nope.

So if I stick my head in the sand, and refuse to believe any of these things exist, does that mean they magically disappear?

It's unfortunate if you've managed to avoid the news for the last decade. The secret prisons the US has been running around the world have been regularly in the news since not long after 9/11.

Also, why are they still considered "secret" if random people on HN are discussing them candidly?

Because their locations are or were undisclosed, and obviously not even everyone here has heard of them. They exist.

Edited in reply They are explicitly said to exist in Hollywood propaganda film Zero Dark Thirty (2013). No, this is not proof, although it is evidence. If the establishment wants us to believe they exist, is that not troubling enough?

FYI hollywood propaganda films aren't usually the best citations...

EDIT: spelling counts...

the fact that the movie made a splash within the security community for "saying too much" helps to give credence, as well.

Yeah, it's a movie, but the people who were upset about it being released were people in authority.

With Hollywood's ties to the US Government, it was probably a fake attempt to get their buddys' movie to sell better...

who knows. theories abound.

For the same reason the Gestapo were the official secrete police of the Nazi Germany. Abbreviation of Geheime Staatspolizei, "Secret State Police"

Or the US Secret Service...