It wasn't intended to be so much a strawman as hyperbole, commenting on certain attitudes. It always bothers me when people speak of cases like this as if everything went well; the evil murderer will be punished, and justice will have been done. No thought is spared for the situation of the obviously mentally unstable perpetrator, and on whether he could have been helped (or god forbid, whether he still could be).
To put it simply, when I look at this case, I don't think "Good, justice was done" but "Man, why did no-one predict this"? And it pains me to see people take glee in the future suffering of the perpetrator, never stopping to consider whether the society has any responsibility for not preventing the crime in the first place.
And lastly, it really annoys me when people say this person should be locked away for life, no chance for parole. The kid is seventeen, and totally messed in the head. With therapy, in 20 or 30 years he could be fixed. He also might not be, but I don't see taking away all chance of freedom, no matter what, as anything but cruelty in the name of a flimsy concept of justice.