Advocates for the idea include ministers, rabbis and a plethora of Op-ed writers. What is interesting about the current writers is that they are not arguing for the moral "Just desserts" argument, but rather for a unique - lets kill them or they will end up being released argument. This is clearly a utilitarian argument - but surely one of the weakest you can make. I'm against the death penalty (as i'm fairly sure is Halacha) except for the most severe and extreme cases. However, I always find utilitarian arguments (i.e inherent danger or the need to set a deterrence) to be lacking. In this specific case, if you are worried about the terrorists being released by a future government, the correct response is either:
A. Grow a backbone, and stop releasing terrorists.
B. Push through legislation that will stop future releases.
C. Make some peace deal that will end the whole mess.
Any of the above would actually suffice - and all are far less extreme than jumping to option D - "Lets kill em all".