But what about the effect of removing criminals from society? Or the perceived harshness in the eyes of the public ("he only got a three week sentence!")?
I think people will learn quickly how harsh solitary confinement is and they can readjust their expectations. Also, the sentence should be moved up meaningfully depending on the level of crime. So 3 weeks for rape would be too little, in my opinion.
People do not commit crimes expecting to be caught. If the death penalty is not a deterrent, how could you expect anything less to be?