It's a country that can arrest and detain without warrant, without charges, without representation and without trial.
That's a gross overstatement. (It's seriously disgusting.) In the United Stats, people don't just get arrested willy-nilly. I'm not saying such a thing has happened, but if you're referencing Gitmo then that's all Afghanistan combatants (weather they really are combatants or not is another debate). Traveling to the United States from another country leaves no possibility of false imprisonment, though you can be detained. When they detain it's usually for a good reason, but just like every place there's idiots who will do it for a clearly innocent person. You just hear the US a lot because people like to hate.
Once you get in to the country, if you are arrested without a warrant, probable cause, and without charges you can expect the prosecution in any kind of trial to get reamed. Believe it or not, our judicial system isn't a bastion of corruption.
When you don't know what to do, walk fast and look worried.