Law doesn't seek to punish but to rehabilitate. Act of taking freedom away from the criminal is violent enough. Treating them badly is just a sign of unfair/poor society that cannot maintain (afford to keep) it's promise to be civil to all citizens.
So the idea is this will rehabilitate Sarkozy? Do you believe that this experience will rehabilitate Sarkozy, or even that he's an active threat to commit more crimes in the future? It seems like the only conceivable social benefit of incarcerating him is to punish him for corruption as a deterrent to others. But his luxury prison room probably won't do that, so it's basically just an expensive legal formality to satisfy public demands for "justice" (ie, retribution for wrongdoing)