Why is waterboarding so bad?

Over the last decade you've probably heard the term "waterboarding" or seen it in a movie at least once or twice.  Here's the wikipedia definition because it's succinct, "Waterboarding is a form of torture in which water is poured over the face of an immobilized captive, thus causing the individual to experience the sensation of drowning."  Often it's shown to be done with a cloth over the person's face.  After doing a little reading on this I found that it was often reported that CIA officers or other trained individuals would last less than 20 seconds before giving up.  One of my first thoughts was is it that quick, can't they just hold their breath for 20 seconds?  Obviously they could, so obviously I was missing something.

After doing some reading it seemed like that number may or may not be true for trained individuals but there have been public demonstrations where it is about right.  There were also some things I learned that weren't obvious to me when I first heard about waterboarding.  One of the key things seems to be that the head of the person is set at a position below their lungs.  This way the water can get into their respiratory system in the mouth and nose but not straight into their lungs, simulating drowning.  So if done right the person is not at a large risk of dying, although it may feel like it to them.

From what I've read it seems like as long as a person can stay in control and hold they're breath they will be ok, but as soon as they lose control of their breathing they're in big trouble.  Some people are better at staying in control than others.  One of the most interesting (and a bit chilling) experiences to read is here.  He talks about testing out waterboarding on himself in a controlled situation.  After his final test he says "It took me ten minutes to recover my senses once I tried this. I was shuddering in a corner, convinced I narrowly escaped killing myself."  Obviously this is anecdotal, but the entire post was very interesting to read.  The conclusion seems to be that at some point our instincts take over and there is nothing we can do to stop the panic.

In an uncontrolled test an interrogator could easily force down a person's chest so that they couldn't hold their breath and combined with the stress of the situation I'm sure that would make it much more difficult.  On top of that this could be done repeatedly and could probably cause severe psychological damage.  So basically you're not going to outlast an interrogator, you will break at some point and holding your breath is not going to help you.

Besides being very cruel, one of the reasons this technique may not be that effective is that it can often bring about false confessions.  If it's anywhere near as terrifying as people have reported you could make anyone confess to anything.