Sadly, when the Supreme Court makes such a decision it becomes gospel for lower courts and few will stand to challenge it, even if the bench looks notably different from when the decision was made. That’s the bad thing about legal precedents, and they just set a big one.
My take is that if one was to rape a child, they know that they are raping a child, particularly a child under 12. If one is to undertake such an act, there is a small chance they don’t know the consequences, but regardless, it is effing WRONG on so many levels as to make distinctions not matter. The death penalty is a serious punishment, and should only be reserved for serious crimes, and I think that in this country we both overuse it and don’t use it enough. Rape can be proven via many means, and since this girl reportedly needed to have surgery afterwards to repair damage, not to mention the ridiculous amount of mental instability she might experience later in life, I can see it being justified here, given sufficient evidence, which the local and supreme courts of Louisiana apparently found.
This is the type of “legislating from the bench” that the courts should not be doing. What they just did may not have created a law for such cases, but it did create a precedent, which sadly in our time, is almost the same thing. They just overturned the laws governing this practice in 5 states. So because he just scarred her for life, and didn’t kill her, he gets to live. That’s fair?
Bravo to both presidential candidates for coming out against the ruling. It doesn’t make much difference at this point, but perhaps something can be done about it once Barack is in office 
footnote: I’m not saying all legal precedents are bad, there area few that I am particularly fond of (Roe v Wade, Epperson v Arkansas, Miranda v Arizona, just to name a few), but as in all imperfect systems, mistakes are made (Dred Scott, and the case in question here, for instance).