Nah, it has been proven to work.
It doesn't work very well, but it still works to some degree, although there are far better and more effective means to reduce criminal activity.
Ah, sorry, I guess I should have been more clear. From what I remember (fairly well, it's only been a few months) that kind of action doesn't actually have much impact on the sort of crimes Monkey was talking about; child molestation, rape, murder, etc. Generally threat of punishment, even great punishment, doesn't even register to the folks committing that sort of act (especially when they're crimes of passion, not premeditation.). There certainly isn't (or wasn't, again, a few months ago) enough statistical correlation to even remotely support it as a viable and effective means to deal with the crimes themselves.
It might work in a few isolated cases (This is what we call an outlier, folks~), but that's (terrifyingly) insufficient for moral justification (And we've got problems if we're basing our justice system off something else.). By that same sort of reasoning, it'd be a good idea to murder literally everyone, because it'd prevent a few crimes. After all, mass murder prevents crimes, right? Bound to kill a few (eventually) guilty folks in there, sooner or later.
... but I'll stop now, I think. I've seen this argument gone over a couple times on this board already