Chemical castration is used for pedophiles as well, and it seems to work somewhat well. Not an emotional argument based on punishment but rather a practical idea, from my point of view.
I also support keeping dangerous criminals off the streets -- who doesn't? but rehabilitation makes more sense than paying to keep them in a prison for the rest of their life for non-murder crimes.
Why not rehabilitation for murder? Most murders are specific in nature. Most murderers are less likely to commit future murders than a serial rapist is to commit future rapes.