>some now wonder how much worse the CIA torture program might actually be
A lot worse. And I'm not talking black sites. CIA has techniques of torture they can use on people without anyone even realizing they're being used. Really nasty, crafty kinds of torture some people never even realize is torture. But, what's the purpose of torture? It isn't to cause harm - this is only the catalyst to the torturer's end goal. The purpose is to coerce a subject into revealing information to someone they might not otherwise.
Of course, if you're strapped down on a table and being electrocuted somewhere in the desert, it's really obvious what's going on, and that the person torturing you wants information. CIA actually intentionally "leaks" information about its torture programs in order to draw people's attention to black sites, waterboarding, and other techniques mostly used against non-Americans.
Sometimes the CIA tortures people just to find out what they do under stress. See if they reveal any patterns in the way they react to stressors. If they observe someone always reacts in a similar way to stress, they might cause harm to that person simply in order to cause them to have that reaction.
And most people to whom it happens never even realize they're being manipulated!