Don't deserve to die? Whether it's a BB gun or sling shot. Such weapons are lethal and when you use it to shoot people. People will retaliate with maximum rage and the outcome is usually always ugly and deadly. I think everyone knows, if you have kids in school that are bullied and beaten often, I believe you wouldn't want your kid to get beaten to a pulp but would want him/her to stand up and fight back. People don't just burst out into a berserker for no reason.
Take it he will be doing life? If more people realize their sentencing after killing a person, I wouldn't be surprise if they go on a rampage spree.