On a purely practical level, I think it'll make rapes less likely to occur. Most rapists are cowards, and if they know they'll be executed for raping women, they'll probably think twice about doing it. Of course, there will always exist those individuals with a total disregard for the law or the consequences of their actions, and they will rape woman. But if you put them to death, they'll never do it again. When you consider that many rapists have multiple victims, you'll understand that executing rapists the first time they're caught can prevent a lot of unnecessary pain.