Some of these prisoners have faced no criminal charges and have never been to see an American court room.
Rendition is seperate from extradition, and therefore does not require a visit to a court room. It's actually more akin to a government agency acting as a bail enforcer. We trade in these favors with other governments. Similar to the three way deal we have with Great Britain and Canada where they listen in on our internet traffic, and we listen in on theirs, then trade reports. It's not illegal for Canada and GB to monitor our citizens, and it's not illegal for the US to get a report on possible criminal activity from Canada or GB. And vice versa. It would be illegal for the US to monitor it's own citizens in this way, and ditto for the other countries, so they don't. Germany and France joined this group as well a few years ago.
Do you think one can abuse extraordinary rendition?
Anything can be abused. And I would hope that any abuse with adequate evidence would be prosecuted. We may get a case soon, Khalid El-Masri has filed against the US and several corporations.