If they're not adults they should not be charged as adults, period. The very fact that doing so is legally possible tells you all you need to know about the Orwellian nightmare that is the US justice system. If you think sentencing caps for juveniles are too low, you can increase them (not that you should, but you can), but that doesn't mean that a 17-year-old magically grows one year older the moment they commit some heinous crime.
If there is no means by which this person can be tried as an adult, how are law-abiding people to be safe from this individual?He's saying there should be something in between, and there should be. I think if anyone is to be tried by the full weight of justice system, they should have a say in it. It is very difficult to say where the line should be, both in terms of the age of the defendant and the maximum penalty. To answer your question more directly, perhaps we should put more emphasis on
corrections (i.e. rehabilitation). We can certainly devise a system that better supports rehabilitation for most people. Not everyone can be rehabilitated or be part of regular society, but we should certainly try.