Because banning the death penalty is equivalent to banning all punishment, right?
It's not banning all punishment, but it is banning the only just punishment for the crime of murder when commited by those under 18.
Yes. If someone has committed a crime that is worthy of death it is because they are too dangerous to be allowed out into society ever again and death is the only means we have to assure that.
You are putting other people at risk. That is not acceptable.
Your cute little snuggle bunny killers did not just happen to kill someone by accident. They either killed multiple victims or they killed in hideous ways.